How to create network connection into remote docker stack?

Question

I am struggling to set this up correctly. I am trying to run an app with docker stack deploy on a remote machine. The following app works, when I deploy it with docker swarm deploy on my windows notebook. But when I run it on the linux cluster. I cannot connect to it. If can help me to identify the missing piece here? When I run the app locally, I get some output from curl localhost:8000, however, not at the remote machine. There I get curl: (7) Failed to connect to localhost port 8000: Connection refused. I also do not understand why I get a different result (app accessible, not accessible) on local and remote computer, i.e. what configuration is the disrupting element.

I tried pruning all the networks and start again from scratch.

First, I connect to a remote server via ssh:

ssh -qy -L 8000:localhost:8000

Here, I start a web application with docker stack, with this simple yaml file testapp.yml:

    version: '3'
    services:
       db:
         image: mysql:5.7
         volumes:
           - db_data:/var/lib/mysql
         restart: always
         environment:
           MYSQL_ROOT_PASSWORD: somewordpress
           MYSQL_DATABASE: wordpress
           MYSQL_USER: wordpress
           MYSQL_PASSWORD: wordpress
    
       wordpress:
         depends_on:
           - db
         image: wordpress:latest
         volumes:
           - web_data:/var/www/html
         ports:
           - "8000:80"
         restart: always
         environment:
           WORDPRESS_DB_HOST: db:3306
           WORDPRESS_DB_USER: wordpress
           WORDPRESS_DB_PASSWORD: wordpress
           WORDPRESS_DB_NAME: wordpress
    
    volumes:
        db_data: {}
        web_data: {}

And deploy this with

docker swarm deploy -c testapp.yml testapp

Now, I get the following output with sudo docker stack services testapp:

ID             NAME                MODE         REPLICAS   IMAGE              PORTS
93rj1ialspj2   testapp_db          replicated   1/1        mysql:5.7          
nl18a7mr4auk   testapp_wordpress   replicated   1/1        wordpress:latest   *:8000->80/tcp

However, when I navigate to localhost:8000there is

This site can’t be reached. localhost refused to connect.

And curl localhost:8000 (on the both systems local and remote) returns

curl: (7) Failed to connect to localhost port 8000: Connection refused

Running docker 20.10.9 remotely and 20.10.8 locally.

Answer 1

First of all, thanks for the drawing so I understand what you are trying.

The next step is, when you are working with Docker Swarm all your stacks/services can hit the external networks like Redis, SQL and S3 storage so that is nothing you need to take care of.

When you want traffic inside your cluster you need a proxy in the front, I personally are using NGINX as proxy layer and then you need to create a upstream with a stack of IP's to your Docker Swarm Manager nodes, never sending it to your workers.

Docker Swarm working the way you are sending traffic to a single port number eg. 9000 and this port 9000 is binding to your stack/services on port 80 or what you are needed. Every single replicate will now running on port 9000 for externel traffic from the managers and into your cluster.

Besure you are deploying your stacks only for worker nodes except if its controller software you needed, else you can get a unstable cluster based on my own expires.

If your Redis and SQL running in the cluster (i hope not) but if you want it, you can setup a network for thoes stacks and the add the network internel into your orther stacks, but i will recommend to keep Redis, SQL and somthing like that on the own servers

So the following up on my description here is you need the following.

• HTTP / HTTPS Proxy to route traffic into a custom port eg. 9000 for your Docker Swarm Managers
• Expose a port eg. 9000 to your service port eg. 80
• Setup connection inside the service to use the external Redis and SQL

Thats it, hope i have explain it good enough else you can just ask :)

Expose sample - Docker

docker run -p 9000:6379 –name redis_cont -d redis

allow port 9000 on your host to route into the redis_cont on port 6379

Expose sample - docker-compose.yml

version: "3.7"
services:

 redis:
    image: "redis:alpine"
    ports:
     - "9000:6379"

Deploy a redis stack into your Docker Swarm and allow port 9000 on your host(Docker Swarm Cluster) to route into the Redis stack service on port 6379