Run a docker container on a specific node in a docker swarm

Question

I have a jenkins pipeline where it build and runs various containers on a NUC server. This NUC is on a cluster (Swarm) with another NUC. I recently added a couple of raspberry Pis on my setup and on that cluster, so now I wonder if there is a way to command Jenknis to deploy on x86_x64 or armhf devices.

I tried the -e constraint:node==<node_name> solution I found on other questions, but i had no luck.

I tried the above command from one x86_x64 node pointing to another and from a x86_x64 node pointing to a armhf node

I dont want to run those containers as a service and i dont care of any load balancer, I just want to run a container on a specific architecture ( x86_x64 or armhf depending on what i want to deploy)

Answer 1

You cannot use constraints on containers, only on services.

That being said, using constraints on services seems a good way to go. You can learn more about services constraints in the official documentation . Here are a few example on how constraints can match node or Docker Engine labels:

# Node ID
node.id==2ivku8v2gvtg4

# Node hostname
node.hostname!=node-2

# Node role
node.role==manager

# Node labels
node.labels.security==high

# Docker Engine's labels
engine.labels.operatingsystem==ubuntu 14.04

If you want to match a specific hostname you need to use node.hostname==<hostname> and not node==<hostname>

You will also want to update the restart_policy key from your service definition deploy policy to prevent from starting a new container once the first one terminates its process successfully.

Wrapping it all together you need something like that:

version: "3.7"
services:
  myapp:
    image: <my_image>
    deploy:
      placement:
        constraints:
          - node.labels.arch == x86_64
      restart_policy:
        condition: on-failure
        delay: 5s
        max_attempts: 3
        window: 120s

Of course, it is up to you to add the labels to each Swarm node. Ansible and its module docker-node are really well suited for this purpose. Here is an example playbook:

- hosts: swarm
  tasks:
    - name: Add label to node specifying architecture 
      docker_node:
        hostname: "{{ inventory_hostname }}"
        labels:
          arch: "{{ ansible_architecture }}"

Your docker nodes would be labelled with the key arch and one of the following values:

• armhf
• armv7l
• i386
• x86_64

Answer 2

Why don't you want to use a service? Services is how we orchestrate things in Swarm. docker container ... will only start/stop/inspect/manipulate things in on a single host. As you already have a swarm cluster set up, why not use a service?