varnish Monitoring Varnish Monitoring backend metrics

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There are a number of metrics describing the communication between Varnish and it's backends.

The most important metrics here might be these:

  • backend_busy - Number of http 5xx statuses recieved by a backend. With VCL you can configure Varnish to try another backend if this happens.
  • backend_fail - Number of times Varnish couldnt connect to the backend. This can have a number of causes (no TCP-connection, long time to first byte, long time between bytes). If this happens your backend isn't healthy.
  • backend_unhealthy - Number of times Varnish couldn't "ping" the backend (it didn't respond with a HTTP 200 response.
varnishstat -1 | grep "backend_"
MAIN.backend_conn           86913481         4.70 Backend conn. success
MAIN.backend_unhealthy             0         0.00 Backend conn. not attempted
MAIN.backend_busy                  0         0.00 Backend conn. too many
MAIN.backend_fail                  7         0.00 Backend conn. failures
MAIN.backend_reuse                 0         0.00 Backend conn. reuses
MAIN.backend_toolate               0         0.00 Backend conn. was closed
MAIN.backend_recycle               0         0.00 Backend conn. recycles
MAIN.backend_retry                 0         0.00 Backend conn. retry
MAIN.backend_req            86961073         4.70 Backend requests made

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