8.2.3. HTTP log format



The HTTP log format is the most complete and the best suited for HTTP proxies. It is enabled by when “option httplog” is specified in the frontend.

It provides the same level of information as the TCP format with additional features which are specific to the HTTP protocol. Just like the TCP format, the log is usually emitted at the end of the session, unless “option logasap” is specified, which generally only makes sense for download sites.

A session which matches the “monitor” rules will never logged. It is also possible not to log sessions for
which no data were sent by the client by specifying “option dontlognull” in the frontend. Successful connections will not be logged if “option dontlog-normal” is specified in the frontend.

Most fields are shared with the TCP log, some being different. A few fields may slightly vary depending on some configuration options. Those ones are marked with a star (‘*’) after the field name below.

Example :

        frontend http-in
            mode http
            option httplog
            log global
            default_backend bck

        backend static
            server srv1 127.0.0.1:8000
    >>> Feb  6 12:14:14 localhost  haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in  static/srv1 10/0/30/69/109 200 2750 - - ---- 1/1/1/1/0 0/0 {1wt.eu} {} "GET /index.html HTTP/1.1"
Field Format Extract from the example above
1 process_name '[' pid ']:' haproxy[14389]:
2 client_ip ':' client_port 10.0.1.2:33317
3 '[' accept_date ']' [06/Feb/2009:12:14:14.655]
4 frontend_name http-in
5 backend_name '/' server_name static/srv1
6 Tq '/' Tw '/' Tc '/' Tr '/' Tt* 10/0/30/69/109
7 status_code 200
8 bytes_read* 2750
9 captured_request_cookie
10 captured_response_cookie
11 termination_state —-
12 actconn '/' feconn '/' beconn '/' srv_conn '/' retries* 1/1/1/1/0
13 srv_queue '/' backend_queue 0/0
14 '{' captured_request_headers* '}' {haproxy.1wt.eu}
15 '{' captured_response_headers* '}' {}
16 '"' http_request '"' GET /index.html HTTP/1.1

Detailed fields description :

  • client_ip” is the IP address of the client which initiated the TCP connection to haproxy. If the connection was accepted on a UNIX socket instead, the IP address would be replaced with the word “unix”. Note that when the connection is accepted on a socket configured with “accept-proxy” and the PROXY protocol is correctly used, then the logs will reflect the forwarded connection’s information.
  • client_port” is the TCP port of the client which initiated the connection. If the connection was accepted on a UNIX socket instead, the port would be replaced with the ID of the accepting socket, which is also reported in the stats interface.
  • accept_date” is the exact date when the TCP connection was received by haproxy (which might be very slightly different from the date observed on the network if there was some queuing in the system’s backlog). This is usually the same date which may appear in any upstream firewall’s log. This does not depend on the fact that the client has sent the request or not.
  • frontend_name” is the name of the frontend (or listener) which received and processed the connection.
  • backend_name” is the name of the backend (or listener) which was selected to manage the connection to the server. This will be the same as the frontend if no switching rule has been applied.
  • server_name” is the name of the last server to which the connection was sent, which might differ from the first one if there were connection errors and a redispatch occurred. Note that this server belongs to the backend which processed the request. If the request was aborted before reaching a server, “<NOSRV>” is indicated instead of a server name. If the request was intercepted by the stats subsystem, “<STATS>” is indicated instead.
  • Tq” is the total time in milliseconds spent waiting for the client to send a full HTTP request, not counting data. It can be “-1” if the connection was aborted before a complete request could be received. It should always be very small because a request generally fits in one single packet. Large times here generally indicate network trouble between the client and haproxy. See “Timers” below for more details.
  • Tw” is the total time in milliseconds spent waiting in the various queues. It can be “-1” if the connection was aborted before reaching the queue. See “Timers” below for more details.
  • Tc” is the total time in milliseconds spent waiting for the connection to establish to the final server, including retries. It can be “-1” if the request was aborted before a connection could be established. See “Timers” below for more details.
  • Tr” is the total time in milliseconds spent waiting for the server to send a full HTTP response, not counting data. It can be “-1” if the request was aborted before a complete response could be received. It generally matches the server’s processing time for the request, though it may be altered by the amount of data sent by the client to the server. Large times here on “GET” requests generally indicate an overloaded server. See “Timers” below for more details.
  • Tt” is the total time in milliseconds elapsed between the accept and the last close. It covers all possible processing. There is one exception, if “option logasap” was specified, then the time counting stops at the moment the log is emitted. In this case, a ‘+’ sign is prepended before the value, indicating that the final one will be larger. See “Timers” below for more details.
  • status_code” is the HTTP status code returned to the client. This status is generally set by the server, but it might also be set by haproxy when the server cannot be reached or when its response is blocked by haproxy.
  • bytes_read” is the total number of bytes transmitted to the client when the log is emitted. This does include HTTP headers. If “option logasap” is specified, the this value will be prefixed with a ‘+’ sign indicating that the final one may be larger. Please note that this value is a 64-bit counter, so log analysis tools must be able to handle it without overflowing.
  • captured_request_cookie” is an optional “name=value” entry indicating that the client had this cookie in the request. The cookie name and its maximum length are defined by the “capture cookie” statement in the frontend configuration. The field is a single dash (‘-‘) when the option is not set. Only one cookie may be captured, it is generally used to track session ID exchanges between a client and a server to detect session crossing between clients due to application bugs. For more details, please consult the section “Capturing HTTP headers and cookies” below.
  • captured_response_cookie” is an optional “name=value” entry indicating that the server has returned a cookie with its response. The cookie name and its maximum length are defined by the “capture cookie” statement in the frontend configuration. The field is a single dash (‘-‘) when the option is not set. Only one cookie may be captured, it is generally used to track session ID exchanges between a client and a server to detect session crossing between clients due to application bugs. For more details, please consult the section “Capturing HTTP headers and cookies” below.
  • termination_state” is the condition the session was in when the session ended. This indicates the session state, which side caused the end of session to happen, for what reason (timeout, error, …), just like in TCP logs, and information about persistence operations on cookies in the last two characters. The normal flags should begin with “–“, indicating the session was closed by either end with no data remaining in buffers. See below “Session state at disconnection” for more details.
  • actconn” is the total number of concurrent connections on the process when the session was logged. It is useful to detect when some per-process system limits have been reached. For instance, if actconn is close to 512 or 1024 when multiple connection errors occur, chances are high that the system limits the process to use a maximum of 1024 file descriptors and that all of them are used. See section 3 “Global parameters” to find how to tune the system.
  • feconn” is the total number of concurrent connections on the frontend when the session was logged. It is useful to estimate the amount of resource required to sustain high loads, and to detect when the frontend’s “maxconn” has been reached. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack.
  • beconn” is the total number of concurrent connections handled by the backend when the session was logged. It includes the total number of concurrent connections active on servers as well as the number of connections pending in queues. It is useful to estimate the amount of additional servers needed to support high loads for a given application. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack.
  • srv_conn” is the total number of concurrent connections still active on the server when the session was logged. It can never exceed the server’s configured “maxconn” parameter. If this value is very often close or equal to the server’s “maxconn”, it means that traffic regulation is involved a lot, meaning that either the server’s maxconn value is too low, or that there aren’t enough servers to process the load with an optimal response time. When only one of the server’s “srv_conn” is high, it usually means that this server has some trouble causing the requests to take longer to be processed than on other servers.
  • retries” is the number of connection retries experienced by this session when trying to connect to the server. It must normally be zero, unless a server is being stopped at the same moment the connection was attempted. Frequent retries generally indicate either a network problem between haproxy and the server, or a misconfigured system backlog on the server preventing new connections from being queued. This field may optionally be prefixed with a ‘+’ sign, indicating that the session has experienced a redispatch after the maximal retry count has been reached on the initial server. In this case, the server name appearing in the log is the one the connection was redispatched to, and not the first one, though both may sometimes be the same in case of hashing for instance. So as a general rule of thumb, when a ‘+’ is present in front of the retry count, this count should not be attributed to the logged server.
  • srv_queue” is the total number of requests which were processed before this one in the server queue. It is zero when the request has not gone through the server queue. It makes it possible to estimate the approximate server’s response time by dividing the time spent in queue by the number of requests in the queue. It is worth noting that if a session experiences a redispatch and passes through two server queues, their positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs.
  • backend_queue” is the total number of requests which were processed before this one in the backend’s global queue. It is zero when the request has not gone through the global queue. It makes it possible to estimate the average queue length, which easily translates into a number of missing servers when divided by a server’s “maxconn” parameter. It is worth noting that if a session experiences a redispatch, it may pass twice in the backend’s queue, and then both positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs.
  • captured_request_headers” is a list of headers captured in the request due to the presence of the “capture request header” statement in the frontend. Multiple headers can be captured, they will be delimited by a vertical bar (‘|’). When no capture is enabled, the braces do not appear, causing a shift of remaining fields. It is important to note that this field may contain spaces, and that using it requires a smarter log parser than when it’s not used. Please consult the section “Capturing HTTP headers and cookies” below for more details.
  • captured_response_headers” is a list of headers captured in the response due to the presence of the “capture response header” statement in the frontend. Multiple headers can be captured, they will be delimited by a vertical bar (‘|’). When no capture is enabled, the braces do not appear, causing a shift of remaining fields. It is important to note that this field may contain spaces, and that using it requires a smarter log parser than when it’s not used. Please consult the section “Capturing HTTP headers and cookies” below for more details.
  • http_request” is the complete HTTP request line, including the method, request and HTTP version string. Non-printable characters are encoded (see below the section “Non-printable characters”). This is always the last field, and it is always delimited by quotes and is the only one which can contain quotes. If new fields are added to the log format, they will be added before this field. This field might be truncated if the request is huge and does not fit in the standard syslog buffer (1024 characters). This is the reason why this field must always remain the last one.
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