CODEWITHSUNDEEP
haproxy
Josh Wilson
Josh Wilson

Reputation: 3755

Haproxy Health Check port

I'm trying to think through the advantages and disadvantages of haproxy health checks happening on a different port from regular traffic.

If a server becomes overloaded having health checks on a different port may mark the server as being up even when overloaded. I think this is a good thing because taking servers offline may make an overloading problem worse, but want to confirm that that makes sense. I can't seem to find any good docs on the tradeoffs though and was wondering if someone has a good analysis on the tradeoffs.

Upvotes: 3

Views: 12854

Answers (1)

anine.io
anine.io

Reputation: 411

The port keyword is often used with address to send health checks somewhere else than directly to the service you are checking. One example might be enabling option httpchk to monitor a non-HTTP service. What you then do is have a HTTP-compatible service that when queried can execute complex health checks against the service you are actually testing.

The above is often done with agent-check nowdays, but some people prefer to use an HTTP interface.

This also has nothing to do with server load, the only idea is to send health checks to some other service, not the one directly monitored, which is more capable of testing the actual service (possibly by using a more-complex logic) and returning a result. As an example, one could have a MySQL backend which instead of being tested just for authentication by option mysql-check, could be tested by a PHP script that, for example, checks if backup is running and if it is returns a 5xx HTTP error. The configuration could be something like:

backend mysql
    mode tcp
    option httpchk GET /mysql-status.php
    server mysqlserver 10.0.0.1:3306 check port 80

Upvotes: 7

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