Session Persistence using Traefik on Docker Swarm Replicas

Question

I trying to implement sticky session on dockers-swarm with traefik, but I could not achieve session persistence over two replicas on same machine. In my docker-compose.yml, I have added labels for traefik and added the loadbalancer as well. Below is my docker-compose.yml, (Although the indentation might not look proper here, but it correct in actual project)

version: '3'

   services:
      web:
        image: php:7.2.11-apache-stretch
        ports:
            - "8080:80"
        volumes:
            - ./code/:/var/www/html/hello/
       stdin_open: true
       tty: true
       deploy:
        mode: replicated
        replicas: 2
        restart_policy:
            condition: any
        update_config:
            delay: 2s
        labels:
            - "traefik.docker.network=docker-test_privnet"
            - "traefik.port=80"
            - "traefik.backend.loadbalancer.sticky=true"
            - "traefik.frontend.rule=PathPrefix:/hello"

    networks:
        - privnet
loadbalancer:
    image: traefik
    command: 
        --docker \
        --docker.swarmmode \
        --docker.watch \
        --web \
        --loglevel=DEBUG
    ports:
        - 80:80
        - 9090:8080
    volumes:
    - /var/run/docker.sock:/var/run/docker.sock
    deploy:
        restart_policy:
            condition: any
        mode: replicated
        replicas: 1
        update_config:
            delay: 2s
        placement:
            constraints: [node.role == manager]

    networks:
        - privnet
networks:
    privnet:
        external: true

Am I missing anything?

Answer 1

A few things.

1. .sticky is deprecated in favor of traefik.backend.loadbalancer.stickiness=true
2. I don't think you need to set the network with traefik.docker.network when you only have a single network connected to that service.
3. Make sure you're testing with a tool that uses cookies, which is how sticky sessions stay sticky. If using curl, be sure to use -c and -b as in this example.
4. I used the voting app sample from my test Swarm setup and added sticky sessions to the "vote" service and it worked for me on a single node. If using a multi-node swarm you'll need the LB in front of multiple swarm nodes to also enable sticky.