Tag Archives: tcplog

8.2.2. TCP log format



The TCP log format is used when “option tcplog” is specified in the frontend, and is the recommended format for pure TCP proxies. It provides a lot of precious information for troubleshooting. Since this format includes timers and byte counts, the log is normally emitted at the end of the session.

It can be emitted earlier if “option logasap” is specified, which makes sense in most environments with long sessions such as remote terminals. Sessions which match the “monitor” rules are never logged.

It is also possible not to emit logs for sessions for which no data were exchanged between the client and the server, by specifying “option dontlognull” in the frontend.

Successful connections will not be logged if “option dontlog-normal” is specified in the frontend. A few fields may slightly vary depending on some configuration options, those are marked with a star (‘*’) after the field name below.

Example :

        frontend fnt
            mode tcp
            option tcplog
            log global
            default_backend bck

        backend bck
            server srv1 127.0.0.1:8000
    >>> Feb  6 12:12:56 localhost haproxy[14387]: 10.0.1.2:33313 [06/Feb/2009:12:12:51.443] fnt bck/srv1 0/0/5007 212 -- 0/0/0/0/3 0/0
Field Format Extract from the example above
1 process_name '[' pid ']:' haproxy[14387]:
2 client_ip ':' client_port 10.0.1.2:33313
3 '[' accept_date ']' [06/Feb/2009:12:12:51.443]
4 frontend_name fnt
5 backend_name '/' server_name bck/srv1
6 Tw '/' Tc '/' Tt* 0/0/5007
7 bytes_read* 212
8 termination_state —-
9 actconn '/' feconn '/' beconn '/' srv_conn '/' retries* 0/0/0/0/3
10 srv_queue '/' backend_queue 0/0

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 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.
  • 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, which is common for TCP applications.
  • 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 connection was aborted before reaching a server, “” is indicated instead of a server name.
  • 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 connection was aborted before a connection could be established. 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.
  • bytes_read” is the total number of bytes transmitted from the server to the client when the log is emitted. 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.
  • 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, and for what reason (timeout, error, …). The normal flags should be “–“, 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 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 connections 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.
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