haproxy.conf

global
    [...]

defaults
    [...]
    
resolvers haproxy-dns
    nameserver dns-server 8.8.8.8:53
    [...]
    accepted_payload_size 8192
    resolve_retries 3
    timeout retry 1s
    hold other 30s
    hold refused 30s
    hold nx 30s
    hold timeout 30s
    hold valid 10s

backend s3_static
    option httpchk HEAD /mybucket/healthcheck.txt HTTP/1.0\r\nHost:\ s3-eu-west-1.amazonaws.com
    http-request set-path /mybucket%[path]
    http-request set-header Host s3-eu-west-1.amazonaws.com
    server s3 s3-eu-west-1.amazonaws.com:80 check inter 15000 fastinter 1000 downinter 1000 rise 1 fall 3 resolvers haproxy-dns init-addr none
    
    
backoffice webapp
    balance roundrobin
    option redispatch
    option httpchk HEAD /healthcheck.txt HTTP/1.0\r\n
    default-server inter 2000 rise 2 fall 3 maxconn 8
    server-template webapp 12 webapp.internal.dns:80 check resolvers haproxy-dns init-addr none