HAProxy (with rsyslogd) and Keepalived in Docker

Quick start

# Start 5 web servers with 2 proxy servers
docker-compose up -d --scale web=5 --scale proxy=2
# show logs of the proxy container
docker-compose logs -f proxy

# Access the virtual IP specified in docker-compose.yml
curl -v 172.18.0.101
# Access Statistics Report
curl -v 172.18.0.101:8080

Testing

# Stop the proxy container in MASTER state
docker stop docker-haproxy_proxy_1
curl -v 172.18.0.101

# Then start it again
#   The priority in keepalived.conf is a random integer so that
#   the container might enter MASTER or BACKUP state which depends
#   on the priority is higher or lower than the priority in another
#   proxy container
docker start docker-haproxy_proxy_1
curl -v 172.18.0.101

Environment

$ cat /etc/redhat-release
CentOS Linux release 7.6.1810

$ docker --version
Docker version 1.13.1, build 7f2769b/1.13.1

$ docker-compose --version
docker-compose version 1.24.1, build 4667896b

$ docker images --format "{{.Repository}}:{{.Tag}}"
docker.io/nginx:1.17.3-alpine
docker.io/haproxy:2.0.7-alpine

Details

• rsyslogd

  • install - apk add rsyslog
  • config - rsyslog.conf
  • define local0 which we will refer in the haproxy.cfg to haproxy.log
  • link haproxy.log to stdout

• HAProxy

  • log to local0 (i.e., stdout)
  • use docker dns resolver
  • response header X-Server to indicate which server was chosen
  • use server-template to initialize multiple servers
  • if haproxy stats access permission denied

• Keepalived

  • install - apk add keepalived
  • config - keepalived.conf
  • automatically determine master/backup by random priority
  • automatically figure out multicast source ip
  • use official entrypoint script
  • according arc-ts' prerequisites
    • should do sysctl net.ipv4.ip_nonlocal_bind=1, but seems not necessary to me
    • host networking parameter --net=host can be configured in docker-compose.yml

Reference

• https://github.com/arc-ts/keepalived
• https://docs.docker.com/v17.09/compose/compose-file/#host-or-none