8. Logging

One of HAProxy’s strong points certainly lies is its precise logs. It probably provides the finest level of information available for such a product, which is very important for troubleshooting complex environments.

Standard information provided in logs include client ports, TCP/HTTP state timers, precise session state at termination and precise termination cause, information about decisions to direct traffic to a server, and of course the ability to capture arbitrary headers.

In order to improve administrators reactivity, it offers a great transparency about encountered problems, both internal and external, and it is possible to send logs to different sources at the same time with different level filters :

  • global process-level logs (system errors, start/stop, etc..)
  • per-instance system and internal errors (lack of resource, bugs, …)
  • per-instance external troubles (servers up/down, max connections)
  • per-instance activity (client connections), either at the establishment or at the termination.

The ability to distribute different levels of logs to different log servers allow several production teams to interact and to fix their problems as soon as possible.

For example, the system team might monitor system-wide errors, while the application team might be monitoring the up/down for their servers in real time, and the security team might analyze the activity logs with one hour

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