Ошибка 502 википедия

From Wikipedia, the free encyclopedia

The 502 Bad Gateway error is an HTTP status code that occurs when a server acting as a gateway or proxy receives an invalid or faulty response from another server in the communication chain.^[1] This error indicates a problem with the communication between the involved servers and can result in disruption of internet services. The 502 Bad Gateway error is considered one of the most common error codes on the internet and can occur in various scenarios.

Specification[edit]

The 502 Bad Gateway error is defined in the RFC 7231 specification, in Section 6.6.3.^[2] The 502 Bad Gateway error is part of the Hypertext Transfer Protocol (HTTP) specification. It is defined in the HTTP/1.1 specification by the World Wide Web Consortium (W3C). According to the specification, the 502 status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an upstream server.

Occurrence[edit]

The 502 Bad Gateway error can occur due to several reasons. Some of the common causes include:^[3]

• Server overload: If a proxy server or gateway is overwhelmed with a large number of requests and is unable to process all of them in a timely manner, it can result in a 502 error. Overload can be caused by high user activity, poor configuration, or inadequate resources on the server.
• Misconfiguration of server infrastructure: A misconfiguration of the server infrastructure, including the proxy server or gateway, can lead to communication problems and trigger the 502 error. For example, invalid DNS settings, firewall restrictions, or inadequate routing rules can result in connection errors between the servers.

• Upstream server failure: If the server that the proxy or gateway is accessing is not functioning properly or experiencing an outage, it can lead to the 502 Bad Gateway error. Failure can occur due to maintenance, hardware issues, software problems, or other technical issues.

• Network issues: Unstable network connections, packet loss, or other network problems can cause communication disruptions between the proxy server and the upstream server. This can result in a 502 error as the proxy server fails to receive a valid response from the upstream server.

Example[edit]

Consider the following example to illustrate the occurrence of a 502 Bad Gateway error:

A user attempts to access a website by entering the URL in their browser.
The user’s request is first received by a proxy server.
The proxy server, acting as an intermediary, forwards the request to an upstream server.
The upstream server processes the request but encounters an internal error.
Instead of sending a valid response, the upstream server sends an invalid or faulty response back to the proxy server.
The proxy server, unable to handle the invalid response, returns a 502 Bad Gateway error to the user’s browser.
The user sees the error page indicating the 502 Bad Gateway status.

References[edit]

External links[edit]

• HTTP status code 502 Bad Gateway at http-statuscode.com
• HTTP 502 Bad Gateway Error Explained at KeyCDN
• HTTP/1.1: Status Code Definitions — World Wide Web Consortium (W3C)
• Troubleshooting 502 Errors — Microsoft Azure
• Common Causes of a 502 Bad Gateway Error and How to Fix It — NGINX

From Wikipedia, the free encyclopedia

This is a list of Hypertext Transfer Protocol (HTTP) response status codes. Status codes are issued by a server in response to a client’s request made to the server. It includes codes from IETF Request for Comments (RFCs), other specifications, and some additional codes used in some common applications of the HTTP. The first digit of the status code specifies one of five standard classes of responses. The optional message phrases shown are typical, but any human-readable alternative may be provided, or none at all.

Unless otherwise stated, the status code is part of the HTTP standard (RFC 9110).

The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes.^[1]

All HTTP response status codes are separated into five classes or categories. The first digit of the status code defines the class of response, while the last two digits do not have any classifying or categorization role. There are five classes defined by the standard:

• 1xx informational response – the request was received, continuing process
• 2xx successful – the request was successfully received, understood, and accepted
• 3xx redirection – further action needs to be taken in order to complete the request
• 4xx client error – the request contains bad syntax or cannot be fulfilled
• 5xx server error – the server failed to fulfil an apparently valid request

1xx informational response

An informational response indicates that the request was received and understood. It is issued on a provisional basis while request processing continues. It alerts the client to wait for a final response. The message consists only of the status line and optional header fields, and is terminated by an empty line. As the HTTP/1.0 standard did not define any 1xx status codes, servers must not^{[note 1]} send a 1xx response to an HTTP/1.0 compliant client except under experimental conditions.

100 Continue

The server has received the request headers and the client should proceed to send the request body (in the case of a request for which a body needs to be sent; for example, a POST request). Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request’s headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body. If the client receives an error code such as 403 (Forbidden) or 405 (Method Not Allowed) then it should not send the request’s body. The response 417 Expectation Failed indicates that the request should be repeated without the Expect header as it indicates that the server does not support expectations (this is the case, for example, of HTTP/1.0 servers).^[2]

101 Switching Protocols

The requester has asked the server to switch protocols and the server has agreed to do so.

102 Processing (WebDAV; RFC 2518)

A WebDAV request may contain many sub-requests involving file operations, requiring a long time to complete the request. This code indicates that the server has received and is processing the request, but no response is available yet.^[3] This prevents the client from timing out and assuming the request was lost. The status code is deprecated.^[4]

103 Early Hints (RFC 8297)

Used to return some response headers before final HTTP message.^[5]

2xx success

This class of status codes indicates the action requested by the client was received, understood, and accepted.^[1]

200 OK

Standard response for successful HTTP requests. The actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource. In a POST request, the response will contain an entity describing or containing the result of the action.

201 Created

The request has been fulfilled, resulting in the creation of a new resource.^[6]

202 Accepted

The request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, and may be disallowed when processing occurs.

203 Non-Authoritative Information (since HTTP/1.1)

The server is a transforming proxy (e.g. a Web accelerator) that received a 200 OK from its origin, but is returning a modified version of the origin’s response.^[7][8]

204 No Content

The server successfully processed the request, and is not returning any content.

205 Reset Content

The server successfully processed the request, asks that the requester reset its document view, and is not returning any content.

206 Partial Content

The server is delivering only part of the resource (byte serving) due to a range header sent by the client. The range header is used by HTTP clients to enable resuming of interrupted downloads, or split a download into multiple simultaneous streams.

207 Multi-Status (WebDAV; RFC 4918)

The message body that follows is by default an XML message and can contain a number of separate response codes, depending on how many sub-requests were made.^[9]

208 Already Reported (WebDAV; RFC 5842)

The members of a DAV binding have already been enumerated in a preceding part of the (multistatus) response, and are not being included again.

226 IM Used (RFC 3229)

The server has fulfilled a request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.^[10]

3xx redirection

This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection.^[1]

A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request. A user agent should detect and intervene to prevent cyclical redirects.^[11]

300 Multiple Choices

Indicates multiple options for the resource from which the client may choose (via agent-driven content negotiation). For example, this code could be used to present multiple video format options, to list files with different filename extensions, or to suggest word-sense disambiguation.

301 Moved Permanently

This and all future requests should be directed to the given URI.

302 Found (Previously «Moved temporarily»)

Tells the client to look at (browse to) another URL. The HTTP/1.0 specification (RFC 1945) required the client to perform a temporary redirect with the same method (the original describing phrase was «Moved Temporarily»),^[12] but popular browsers implemented 302 redirects by changing the method to GET. Therefore, HTTP/1.1 added status codes 303 and 307 to distinguish between the two behaviours.^[11]

303 See Other (since HTTP/1.1)

The response to the request can be found under another URI using the GET method. When received in response to a POST (or PUT/DELETE), the client should presume that the server has received the data and should issue a new GET request to the given URI.

304 Not Modified

Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. In such case, there is no need to retransmit the resource since the client still has a previously-downloaded copy.

305 Use Proxy (since HTTP/1.1)

The requested resource is available only through a proxy, the address for which is provided in the response. For security reasons, many HTTP clients (such as Mozilla Firefox and Internet Explorer) do not obey this status code.

306 Switch Proxy

No longer used. Originally meant «Subsequent requests should use the specified proxy.»

307 Temporary Redirect (since HTTP/1.1)

In this case, the request should be repeated with another URI; however, future requests should still use the original URI. In contrast to how 302 was historically implemented, the request method is not allowed to be changed when reissuing the original request. For example, a POST request should be repeated using another POST request.

308 Permanent Redirect

This and all future requests should be directed to the given URI. 308 parallel the behaviour of 301, but does not allow the HTTP method to change. So, for example, submitting a form to a permanently redirected resource may continue smoothly.

4xx client errors

This class of status code is intended for situations in which the error seems to have been caused by the client. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents should display any included entity to the user.

400 Bad Request

The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax, size too large, invalid request message framing, or deceptive request routing).

401 Unauthorized

Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication. 401 semantically means «unauthorised», the user does not have valid authentication credentials for the target resource.

Some sites incorrectly issue HTTP 401 when an IP address is banned from the website (usually the website domain) and that specific address is refused permission to access a website.^{[citation needed]}

402 Payment Required

Reserved for future use. The original intention was that this code might be used as part of some form of digital cash or micropayment scheme, as proposed, for example, by GNU Taler,^[14] but that has not yet happened, and this code is not widely used. Google Developers API uses this status if a particular developer has exceeded the daily limit on requests.^[15] Sipgate uses this code if an account does not have sufficient funds to start a call.^[16] Shopify uses this code when the store has not paid their fees and is temporarily disabled.^[17] Stripe uses this code for failed payments where parameters were correct, for example blocked fraudulent payments.^[18]

403 Forbidden

The request contained valid data and was understood by the server, but the server is refusing action. This may be due to the user not having the necessary permissions for a resource or needing an account of some sort, or attempting a prohibited action (e.g. creating a duplicate record where only one is allowed). This code is also typically used if the request provided authentication by answering the WWW-Authenticate header field challenge, but the server did not accept that authentication. The request should not be repeated.

404 Not Found

The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.

405 Method Not Allowed

A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.

406 Not Acceptable

The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request. See Content negotiation.

407 Proxy Authentication Required

The client must first authenticate itself with the proxy.

408 Request Timeout

The server timed out waiting for the request. According to HTTP specifications: «The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.»

409 Conflict

Indicates that the request could not be processed because of conflict in the current state of the resource, such as an edit conflict between multiple simultaneous updates.

410 Gone

Indicates that the resource requested was previously in use but is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource in the future. Clients such as search engines should remove the resource from their indices. Most use cases do not require clients and search engines to purge the resource, and a «404 Not Found» may be used instead.

411 Length Required

The request did not specify the length of its content, which is required by the requested resource.

412 Precondition Failed

The server does not meet one of the preconditions that the requester put on the request header fields.

413 Payload Too Large

The request is larger than the server is willing or able to process. Previously called «Request Entity Too Large» in RFC 2616.^[19]

414 URI Too Long

The URI provided was too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request. Called «Request-URI Too Long» previously in RFC 2616.^[20]

415 Unsupported Media Type

The request entity has a media type which the server or resource does not support. For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.

416 Range Not Satisfiable

The client has asked for a portion of the file (byte serving), but the server cannot supply that portion. For example, if the client asked for a part of the file that lies beyond the end of the file. Called «Requested Range Not Satisfiable» previously RFC 2616.^[21]

417 Expectation Failed

The server cannot meet the requirements of the Expect request-header field.^[22]

418 I’m a teapot (RFC 2324, RFC 7168)

This code was defined in 1998 as one of the traditional IETF April Fools’ jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers. The RFC specifies this code should be returned by teapots requested to brew coffee.^[23] This HTTP status is used as an Easter egg in some websites, such as Google.com’s «I’m a teapot» easter egg.^[24][25][26] Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden.^[27][28]

421 Misdirected Request

The request was directed at a server that is not able to produce a response (for example because of connection reuse).

422 Unprocessable Entity

The request was well-formed but was unable to be followed due to semantic errors.^[9]

423 Locked (WebDAV; RFC 4918)

The resource that is being accessed is locked.^[9]

424 Failed Dependency (WebDAV; RFC 4918)

The request failed because it depended on another request and that request failed (e.g., a PROPPATCH).^[9]

425 Too Early (RFC 8470)

Indicates that the server is unwilling to risk processing a request that might be replayed.

426 Upgrade Required

The client should switch to a different protocol such as TLS/1.3, given in the Upgrade header field.

428 Precondition Required (RFC 6585)

The origin server requires the request to be conditional. Intended to prevent the ‘lost update’ problem, where a client GETs a resource’s state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.^[29]

429 Too Many Requests (RFC 6585)

The user has sent too many requests in a given amount of time. Intended for use with rate-limiting schemes.^[29]

431 Request Header Fields Too Large (RFC 6585)

The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large.^[29]

451 Unavailable For Legal Reasons (RFC 7725)

A server operator has received a legal demand to deny access to a resource or to a set of resources that includes the requested resource.^[30] The code 451 was chosen as a reference to the novel Fahrenheit 451 (see the Acknowledgements in the RFC).

5xx server errors

The server failed to fulfil a request.

Response status codes beginning with the digit «5» indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.

500 Internal Server Error

A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.

501 Not Implemented

The server either does not recognize the request method, or it lacks the ability to fulfil the request. Usually this implies future availability (e.g., a new feature of a web-service API).

502 Bad Gateway

The server was acting as a gateway or proxy and received an invalid response from the upstream server.

503 Service Unavailable

The server cannot handle the request (because it is overloaded or down for maintenance). Generally, this is a temporary state.^[31]

504 Gateway Timeout

The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.

505 HTTP Version Not Supported

The server does not support the HTTP version used in the request.

506 Variant Also Negotiates (RFC 2295)

Transparent content negotiation for the request results in a circular reference.^[32]

507 Insufficient Storage (WebDAV; RFC 4918)

The server is unable to store the representation needed to complete the request.^[9]

508 Loop Detected (WebDAV; RFC 5842)

The server detected an infinite loop while processing the request (sent instead of 208 Already Reported).

510 Not Extended (RFC 2774)

Further extensions to the request are required for the server to fulfil it.^[33]

511 Network Authentication Required (RFC 6585)

The client needs to authenticate to gain network access. Intended for use by intercepting proxies used to control access to the network (e.g., «captive portals» used to require agreement to Terms of Service before granting full Internet access via a Wi-Fi hotspot).^[29]

Unofficial codes

The following codes are not specified by any standard.

218 This is fine (Apache HTTP Server)

Used by Apache servers. A catch-all error condition allowing the passage of message bodies through the server when the ProxyErrorOverride setting is enabled. It is displayed in this situation instead of a 4xx or 5xx error message.^[34]

419 Page Expired (Laravel Framework)

Used by the Laravel Framework when a CSRF Token is missing or expired.^{[citation needed]}

420 Method Failure (Spring Framework)

A deprecated response used by the Spring Framework when a method has failed.^[35]

420 Enhance Your Calm (Twitter)

Returned by version 1 of the Twitter Search and Trends API when the client is being rate limited; versions 1.1 and later use the 429 Too Many Requests response code instead.^[36] The phrase «Enhance your calm» comes from the 1993 movie Demolition Man, and its association with this number is likely a reference to cannabis.^{[citation needed]}

430 Request Header Fields Too Large (Shopify)

Used by Shopify, instead of the 429 Too Many Requests response code, when too many URLs are requested within a certain time frame.^[37]

450 Blocked by Windows Parental Controls (Microsoft)

The Microsoft extension code indicated when Windows Parental Controls are turned on and are blocking access to the requested webpage.^[38]

498 Invalid Token (Esri)

Returned by ArcGIS for Server. Code 498 indicates an expired or otherwise invalid token.^[39]

499 Token Required (Esri)

Returned by ArcGIS for Server. Code 499 indicates that a token is required but was not submitted.^[39]

509 Bandwidth Limit Exceeded (Apache Web Server/cPanel)

The server has exceeded the bandwidth specified by the server administrator; this is often used by shared hosting providers to limit the bandwidth of customers.^[40]

529 Site is overloaded

Used by Qualys in the SSLLabs server testing API to signal that the site can’t process the request.^[41]

530 Site is frozen

Used by the Pantheon Systems web platform to indicate a site that has been frozen due to inactivity.^[42]

598 (Informal convention) Network read timeout error

Used by some HTTP proxies to signal a network read timeout behind the proxy to a client in front of the proxy.^[43]

599 Network Connect Timeout Error

An error used by some HTTP proxies to signal a network connect timeout behind the proxy to a client in front of the proxy.

Internet Information Services

Microsoft’s Internet Information Services (IIS) web server expands the 4xx error space to signal errors with the client’s request.

440 Login Time-out

The client’s session has expired and must log in again.^[44]

449 Retry With

The server cannot honour the request because the user has not provided the required information.^[45]

451 Redirect

Used in Exchange ActiveSync when either a more efficient server is available or the server cannot access the users’ mailbox.^[46] The client is expected to re-run the HTTP AutoDiscover operation to find a more appropriate server.^[47]

IIS sometimes uses additional decimal sub-codes for more specific information,^[48] however these sub-codes only appear in the response payload and in documentation, not in the place of an actual HTTP status code.

nginx

The nginx web server software expands the 4xx error space to signal issues with the client’s request.^[49][50]

444 No Response

Used internally^[51] to instruct the server to return no information to the client and close the connection immediately.

494 Request header too large

Client sent too large request or too long header line.

495 SSL Certificate Error

An expansion of the 400 Bad Request response code, used when the client has provided an invalid client certificate.

496 SSL Certificate Required

An expansion of the 400 Bad Request response code, used when a client certificate is required but not provided.

497 HTTP Request Sent to HTTPS Port

An expansion of the 400 Bad Request response code, used when the client has made a HTTP request to a port listening for HTTPS requests.

499 Client Closed Request

Used when the client has closed the request before the server could send a response.

Cloudflare

Cloudflare’s reverse proxy service expands the 5xx series of errors space to signal issues with the origin server.^[52]

520 Web Server Returned an Unknown Error

The origin server returned an empty, unknown, or unexpected response to Cloudflare.^[53]

521 Web Server Is Down

The origin server refused connections from Cloudflare. Security solutions at the origin may be blocking legitimate connections from certain Cloudflare IP addresses.

522 Connection Timed Out

Cloudflare timed out contacting the origin server.

523 Origin Is Unreachable

Cloudflare could not reach the origin server; for example, if the DNS records for the origin server are incorrect or missing.

524 A Timeout Occurred

Cloudflare was able to complete a TCP connection to the origin server, but did not receive a timely HTTP response.

525 SSL Handshake Failed

Cloudflare could not negotiate a SSL/TLS handshake with the origin server.

526 Invalid SSL Certificate

Cloudflare could not validate the SSL certificate on the origin web server. Also used by Cloud Foundry’s gorouter.

527 Railgun Error

Error 527 indicates an interrupted connection between Cloudflare and the origin server’s Railgun server.^[54]

530

Error 530 is returned along with a 1xxx error.^[55]

AWS Elastic Load Balancing

Amazon Web Services’ Elastic Load Balancing adds a few custom return codes to signal issues either with the client request or with the origin server.^[56]

460

Client closed the connection with the load balancer before the idle timeout period elapsed. Typically when client timeout is sooner than the Elastic Load Balancer’s timeout.^[56]

463

The load balancer received an X-Forwarded-For request header with more than 30 IP addresses.^[56]

464

Incompatible protocol versions between Client and Origin server.^[56]

561 Unauthorized

An error around authentication returned by a server registered with a load balancer. You configured a listener rule to authenticate users, but the identity provider (IdP) returned an error code when authenticating the user.^[56]

Caching warning codes (obsoleted)

The following caching related warning codes were specified under RFC 7234. Unlike the other status codes above, these were not sent as the response status in the HTTP protocol, but as part of the «Warning» HTTP header.^[57][58]

Since this «Warning» header is often neither sent by servers nor acknowledged by clients, this header and its codes were obsoleted by the HTTP Working Group in 2022 with RFC 9111.^[59]

110 Response is Stale

The response provided by a cache is stale (the content’s age exceeds a maximum age set by a Cache-Control header or heuristically chosen lifetime).

111 Revalidation Failed

The cache was unable to validate the response, due to an inability to reach the origin server.

112 Disconnected Operation

The cache is intentionally disconnected from the rest of the network.

113 Heuristic Expiration

The cache heuristically chose a freshness lifetime greater than 24 hours and the response’s age is greater than 24 hours.

199 Miscellaneous Warning

Arbitrary, non-specific warning. The warning text may be logged or presented to the user.

214 Transformation Applied

Added by a proxy if it applies any transformation to the representation, such as changing the content encoding, media type or the like.

299 Miscellaneous Persistent Warning

Same as 199, but indicating a persistent warning.

See also

• Custom error pages
• List of FTP server return codes
• List of HTTP header fields
• List of SMTP server return codes
• Common Log Format

Explanatory notes

References

External links

• «RFC 9110: HTTP Semantics and Content, Section 15 «Status Codes»«.
• Hypertext Transfer Protocol (HTTP) Status Code Registry at the Internet Assigned Numbers Authority
• HTTP status codes at http-statuscode.com
• MDN status code reference at mozilla.org

502 Bad Gateway (с англ. плохой шлюз) — ошибка, которую выдают интернет-сайты в случае, если появились проблемы на стороне сайта, касающиеся работы прокси-сервера, DNS-сервера или хостинг-сервера. Принадлежит к ошибкам серии 5xx, которые обычно означают проблемы на стороне сервера.

[править] Действия при ошибке 502

• Проверить, имеется ли доступ к Интернету (зайти на любой другой сайт).
  • Если проблем с доступом нет — можно удалить файлы cookies.
• Если указанное выше не помогло — проблема на стороне сервера. Следует обратиться к системному администратору сайта.

Одной из типичных причин возникновения 502-й ошибки является прекращение работы бекенда при работающем фронтенде сайта.

[править] Ошибка 502 на крупных сайтах

• Ошибка 502 появлялась, когда не работали сервисы Гугла в декабре 2011 года.

[править] См. также

• 500
• 503
• 504

[править] Ссылки

• Ошибка 502 Bad Gateway

О чем речь? Если сервер, с которым связывается ваше устройство, получает некорректный ответ от сервера уровнем выше, на экране компьютера или смартфона высвечивается ошибка 502 Bad Gateway, делая работу невозможной.

На что обратить внимание? Проблема чаще всего возникает из-за сбоев в функциях DNS, прокси или хостинга. Но ситуация поправима, причем сделать это может не только администратор ресурса. Зачастую хватает и грамотных действий обычного пользователя.

Общая характеристика ошибки 502 Bad Gateway

Любой сайт состоит из большого количества файлов: CSS-стили, коды, медиаконтент, HTML-документы и т. д. Все эти данные хранятся на веб-сервере. Чтобы открыть страницу и получить доступ к контенту, браузер направляет запрос на сервер. Если ответ на него по каким-либо причинам не поступает, появляется ошибка сервера 502.

В переводе ошибка 502 Bad Gateway означает «плохой шлюз», соответственно, проблема на шлюзе, в роли которого выступает прокси-сервер. То есть баг возникает в случае, если прокси не может получить данные от источника. Код состояния HTTP 502 веб-сервер использует для описания ошибки.

Проблема может распространяться как на весь сайт полностью, так и на отдельные его страницы. В зависимости от программы, которая была использована для создания веб-сервера, у ошибки 502 есть две основные разновидности – Bad Gateway Nginx или Bad Gateway Apache. Причины возникновения проблемы при этом одинаковы.

Также эта ошибка может иметь и другие формулировки:

• Error 502.
• Bad 502 Gateway.
• 502 Error.
• 502 Proxy Error.
• Bad Gateway: Registered endpoint failed to handle the request, Temporary Error (502).
• That’s an error.
• 502 Service Temporarily Overloaded.
• 502 Server Error: The server encountered a temporary error and could not complete your request.
• 502 – Web server received an invalid response while acting as a gateway or proxy server.
• HTTP 502.
• HTTP Error 502 Bad Gateway.

Между сервером и браузером может стоять веб-сервер, который хранит файлы сайта и используется для снижения нагрузки. Он находит необходимую страницу в каталоге и отправляет ее в ответ на запрос пользователя. Обозреватель обрабатывает полученный файл и отображает его на экране. Так как веб-сервер выступает посредником между браузером и сервером, то именно он оповещает пользователя о проблеме.

Чаще всего причиной ошибки 502 при открытии сайта является перегрузка сервера, которая может возникнуть по ряду причин:

• Большое количество посетителей одновременно. Возможности сервера ограничены, потому просматривать сайт может лишь определенное количество пользователей. Максимальное число зависит от мощности сервера и настроек, которые установил владелец ресурса. Если одновременно на сайт зайдет слишком большое количество пользователей, то сервер не выдержит нагрузку, и страница выдаст код ошибки 502. Например, такие ситуации часто случаются в интернет-магазинах в период акций и сезонных распродаж.
• Хакерская атака (DDoS-атака). Хакеры, создавая большое количество запросов, имитируют огромный наплыв пользователей, вследствие чего сервер перегружается и выходит из строя.

• Плохая оптимизация сайта. Если настройки площадки выставлены таким образом, что небольшое количество посетителей генерирует много запросов, то в таком случае следует оптимизировать работу сервера с пользователями.
• Действия соседей по виртуальному хостингу. Если вы пользуетесь виртуальным хостингом, то мощность веб-сервера делится на всех его арендаторов. В случае возникновения проблем у одного из сайтов возрастет потребляемая им мощность. Оставшейся части ресурсов может быть недостаточно для корректной работы других участников хостинга, и сайт выдаст номер ошибки 502.

Еще одной причиной возникновения такого бага может быть некорректная работа PHP-скрипта. Неверно настроенные плагины могут выдавать ошибку сайта 502.

Также причиной может являться баг браузера. Проблема может быть на стороне пользователя в случае, если у него установлены расширения, нарушающие соединение с сервером сайта.

Советы пользователю по исправлению ошибки 502

Ошибка 502: что делать?

• Перезагрузите страницу. В случае если проблема возникла по причине большого наплыва посетителей, через некоторое время количество пользователей может сократиться, и сайт начнет работать корректно.
• Проверьте подключение к сети Интернет. Браузер может не получать данные с сервера из-за нестабильного соединения или низкой скорости. Попробуйте перезагрузить роутер или отключите его на некоторое время от электросети.

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• Попытайтесь зайти на другой сайт, чтобы убедиться, что проблема не в настройках вашего устройства. Если вы сможете зайти на иную площадку, значит, ошибка возникла со стороны владельца веб-ресурса. Вы сможете попасть на нужную страницу, когда администратор восстановит доступ.
• Почистите файлы cookies. Если при повторном входе на сайт по-прежнему отображается ошибка 502, попробуйте очистить кэш браузера. Возможно, доступ уже был восстановлен, но ваш обозреватель обращается к старой версии страницы из памяти.

• Попробуйте другой сервис. Если ошибка при открытии сайта возникает только на одном устройстве, возможно, проблема в настройках конкретной программы. Решить ее может помочь использование другого браузера.
• Отключите расширения и плагины. Причиной ошибки могут быть плагины и расширения (особенно для работы с прокси- и VPN-сервисами), которые блокируют доступ к некоторым сайтам. Попробуйте отключить их и снова зайти на страницу.
• Очистите кэш DNS. DNS-кэш – это своего рода база данных, которая временно хранит IP-адреса ранее посещенных сайтов с вашего компьютера, чтобы впоследствии они загружались быстрее. При смене DNS данные из памяти будут отправлять по старому пути, и в браузере появится код ошибки 502. После очистки кэша сервис будет обращаться уже к новому IP-адресу.

Ниже приведены инструкции для разных операционных систем:

• В Windows 10, чтобы избавиться от ошибки 502, комбинацией клавиш Win+R откройте командную строку, введите «cmd» и нажмите OK. В открывшемся окне наберите команду ipconfig /flushdns и нажмите Enter. Дождитесь оповещения об успешной очистке кэша.
• В Windows 7 в консоли введите команду ipconfig /flushdns и нажмите Enter. Затем выполните команды net stop dnscache и net start dnscache, чтобы перезапустить службу DNS-клиента.
• В macOS нажмите на иконку поиска в правом верхнем углу и напишите «Терминал», кликните по найденному приложению. В открывшемся окне введите команду sudo killall -HUP mDNSResponder.
• В Linux запустите терминал из основного меню или сочетанием клавиш Ctrl + Alt + T. Для Ubuntu – введите команду sudo service network-manager restart и нажмите Enter (иногда она работает и на других дистрибутивах). Для иных вариантов попробуйте sudosystem-resolve –flush-caches или sudo /etc/init.d/nscd restart.

В некоторых дистрибутивах может потребоваться запуск других команд.

• Измените DNS-сервер по умолчанию. Данное действие может повысить безопасность и скорость. Для этого в настройках роутера нужно указать адреса публичных DNS-серверов.
• Свяжитесь с администратором. Если у вас есть контакты администратора сайта, расскажите ему об ошибке, с которой столкнулись. Возможно, он еще не в курсе проблемы и, соответственно, пока не решает ее.

Рекомендации администратору по исправлению ошибки 502

В первую очередь необходимо проверить журнал ошибок

В WordPress он расположен в папке wp-content, имя файла debug.log. Если такого файла нет или он пустой, то нужно включить запись логов в конфигурационном файле wp-config.php.

Если у вас VPS/VDS или выделенный сервер, нужно дополнительно посмотреть логи сервера. Это поможет определить:

• влияют ли обновления на сервере на возникновение ошибки 502;
• признаки DDoS-атаки (массовые однотипные запросы);
• подозрительную активность с некоторых IP-адресов;
• отсутствие соединения между вашими серверами Nginx, Apache и т. д.

По результатам проверки можно предпринимать действия для решения возникшей проблемы.

Использование команды top

Исправление ошибки 502 на виртуальном сервере можно начать с проверки командой top (на виртуальном хостинге такой вариант чаще всего недоступен).

Проверка может выявить следующие причины возникшей проблемы:

• Недостаточно памяти сервера. На это укажет аббревиатура OOM (out of memory) в результатах или же в параметре Mem – free (свободная память) будет слишком маленькое число.
• Если ошибка 502 по причине нехватки памяти возникает все чаще, вероятно, посещаемость площадки выросла, и вам нужно увеличить на сервере объем оперативной памяти или выбрать другой тариф.
• Недостаточно лимита php-cgi процессов для обработки запросов пользователей. Возможно, установлены слишком маленькие лимиты. Попробуйте их увеличить в конфигурационном файле httpd.conf.

Проверьте плагины в WordPress

Если ваш сайт создан на WordPress, некоторые плагины и темы могут влиять на работу сервера. Войдите в панель управления. Если вы пользуетесь услугой REG.Site, сделать это можно из личного кабинета. Перейдите во вкладку «Плагины» –«Установленные». Нажмите «Деактивировать» у того, который, по вашему мнению, повлиял на работу сайта.

Можно отключить сразу все плагины, чтобы убедиться, что один из них действительно мешает. И далее по очереди включать по одному, пока не обнаружите тот самый, по вине которого возникает ошибка.

Проверьте, как работают вспомогательные службы, например, MySQL и Memcached

Порой они могут быть причиной ошибки 502.

Попробуйте отключить анти-DDoS

Часто хостинги предлагают готовые инструменты, которые предупреждают DDoS-атаки, перенаправляя трафик посетителей на специальные серверы. Там DDoS-запросы отделяются от реальных, и вашему ресурсу передаются уже очищенные. Если в этой последовательности процессов происходит какой-то сбой, то возникает ошибка 502. Чтобы устранить проблему, попробуйте временно отключить анти-DDoS.

Увеличьте количество ресурсов

Нехватка мощности хостинга, на котором размещен сайт, может быть причиной ошибки 502. Особенно часто такое возникает при использовании виртуальных серверов. Если при работе сайта вы превышаете ограничения тарифного плана, хостинг разрывает соединение.

Обычно информацию об этом можно найти в логах. В этом случае нужно арендовать сервер с большим количеством процессоров и оперативной памяти.

Попросите помощи у коллег

Поищите решение проблемы в FAQ вашего провайдера или на Stack Overflow. Вероятнее всего, вы не первый, кто столкнулся с подобной ситуацией, и рабочий вариант исправления бага уже описан. Если же найденные в Интернете советы не окажутся полезными, вы можете создать свою тему на форуме или попросить помощи у более опытных коллег.

Свяжитесь со службой поддержки своего хостинг-провайдера и подробно опишите проблему и все действия, которые были предприняты.

Если и это не помогло, стоит обратиться за консультацией к специалисту

Он проанализирует проблему, выяснит причину возникновения ошибки и устранит ее.

Появление ошибки 502 Bad Gateway – нередкий случай. Справиться с ней могут как специалисты, так и пользователи сайта. Регулярная оптимизация веб-ресурсов положительно скажется на их работе и доступности.