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techraf
Asked: 2017-01-01 04:04:45 +0800 CST

CoreOS: how to set dependencies for Docker containers in cloud-config?

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I have a basic cloud-config.yaml to run four containers on CoreOS (directly, without clustering). Two of the containers (nginx-gen and nginx-letsencrypt) mount volumes from the container named nginx. Each container startup is defined as a systemd unit.

I have added After= and Requires= dependencies, however upon first login I am greeted with:

CoreOS stable (1185.5.0)
Failed Units: 2
  letsencrypt.service
  nginx-gen.service

nginx (the one providing volume) is running.

If after that I execute:

sudo systemctl start nginx-gen.service
sudo systemctl start letsencrypt.service

They start and run correctly, so I guess the problem is in dependencies at the system startup.

I am not experienced with CoreOS nor systemd, so the cause may be pretty basic (like the unit getting "complete"-status before Docker container actually runs).

And looking at the journalctl log, indeed the nginx-gen service fails before it has a chance to mount volumes from nginx:

...
Jan 02 14:35:47 core-01 systemd[1]: nginx-gen.service: Failed with result 'start-limit-hit'.
...
Jan 02 14:36:03 core-01 docker[1401]: Status: Downloaded newer image for nginx:latest
...

What can I do to fix the problem?

My cloud-config.yaml:

#cloud-config

write_files:  
  # omitted for ServerFault: ensure template file
  #   https://raw.githubusercontent.com/jwilder/nginx-proxy/master/nginx.tmpl)
  #   and directories (/path/to/templates, /path/to/certs) are in-place

coreos:
  units:
    - name: nginx.service
      command: start
      content: |
        [Unit]
        Description=Generic Nginx container

        [Service]
        Restart=always
        ExecStart=/usr/bin/docker run --name nginx -p 80:80 -p 443:443 -v /etc/nginx/conf.d -v /etc/nginx/vhost.d -v /usr/share/nginx/html -v /path/to/certs:/etc/nginx/certs:ro nginx
        ExecStop=/usr/bin/docker rm -f nginx

    - name: nginx-gen.service
      command: start
      content: |
        [Unit]
        Description=Docker-gen service for Nginx

        After=nginx.service
        Requires=nginx.service

        [Service]
        Restart=always
        ExecStart=/usr/bin/docker run --name nginx-gen --volumes-from nginx -v /path/to/templates:/etc/docker-gen/templates -v /path/to/certs:/etc/nginx/certs:ro -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/docker-gen -notify-sighup nginx -watch -wait 5s:30s /etc/docker-gen/templates/nginx.tmpl /etc/nginx/conf.d/default.conf
        ExecStop=/usr/bin/docker rm -f nginx-gen

    - name: letsencrypt.service
      command: start
      content: |
        [Unit]
        Description=Ngnix reverse proxy Letsencrypt companion

        After=nginx.service
        Requires=nginx.service

        [Service]
        Restart=always
        ExecStart=/usr/bin/docker run --name nginx-letsencrypt -e "NGINX_DOCKER_GEN_CONTAINER=nginx-gen" --volumes-from nginx -v /path/to/certs:/etc/nginx/certs:rw -v /var/run/docker.sock:/var/run/docker.sock:ro jrcs/letsencrypt-nginx-proxy-companion
        ExecStop=/usr/bin/docker rm -f nginx-letsencrypt
docker systemd coreos

1 Answers

  1. Per http://container-solutions.com/running-docker-containers-with-systemd/, you need to enforce that these containers launch after the docker service.

    Sample:

    [Unit]
Description=Redis Container
After=docker.service
Requires=docker.service

[Service]
TimeoutStartSec=0
Restart=always
ExecStartPre=-/usr/bin/docker stop %n
ExecStartPre=-/usr/bin/docker rm %n
ExecStartPre=/usr/bin/docker pull redis
ExecStart=/usr/bin/docker run --rm --name %n redis

[Install]
WantedBy=multi-user.target

    So in your case, adding Requires=docker.service to the Unit section of your nginx unit should do it, and probably add a WantedBy to each of your units as well so SystemD knows to run them.

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