Haproxy: use backend server like backup

Question

To my haproxy i redirect the traffic to single server in backend, i need set another server what work only in case of failure of first server, it's possible? I read the guide, but in balance algorithm don't have found any answer

Answer 1

Yes it's possible, i set a backup server adding backup after check like this:

backend test
 server 01 10.0.0.1:80 check
 server 02 10.0.0.2:80 check backup

Answer 2

There is an article in their blog about how to implement such setup. My config looks like this:

...
frontend http-1080
  mode http
  bind :1080

  # Enable http access logs
  no option dontlog-normal
  option log-separate-error

  default_backend http-80-app

backend http-80-app
  balance roundrobin
  mode http
  option forwardfor if-none
  option httpchk GET /site/health-check "HTTP/1.1\r\nHost: example.com\r\nAuthorization: Basic thebase64hash=="
  retry-on conn-failure empty-response 500 502 503 504
  http-reuse always
  option allbackups

  default-server inter 3s fall 2 rise 2

  server lb01-hel1-80 4.1.5.133:80 check
  server lb02-hel1-80 4.1.5.134:80 check
  server fe01-lim1-80 1.7.4.3:80 check backup
  server fe02-lim1-80 1.7.4.4:80 check backup

for HTTPS the server string looks like this:

  server lb01-hel1-443 4.1.5.133:443 check ssl sni str(example.com) verify none
  ...
  server fe01-lim1-443 1.7.4.3:443 check ssl sni str(example.com) verify none backup
  ...