Deploying Applications With Docker-Swarm.

Applications Deployment With Docker Swarm

Docker Swarm orchestrates your Docker Engines across multiple hosts. Simply define your applications as service stacks, and Swarm handles the deployment and management. Think docker-compose for the whole team! But what happens under the hood?

This captures the core idea of Swarm - simplified orchestration through service stacks - without getting bogged down in technical details like file formats. It also retains the connection to docker-compose, but avoids going off on a tangent about configuration similarities.

Lets' get our hands dirty

You can work with your own server to code along but I highly recommend using play-with-docker.com. It is a website managed by a few smart Docker developers. It comes with Docker preinstalled and configured. You can spin up several node servers for a restricted duration.

Creating Our Docker Swarm

docker swarm init --advertise-addr <your node_ip >        

Substitute <your node_ip> with the IP address of your node. On play-with-docker website, the address of your IP is on the top page, and if you’re using your own VPS, feel free to use your server’s private IP address as long as it is accessible by other nodes.

docker swarm join-token manager        

Copy the command you just generated and run it on both your second and third nodes. This will bring those nodes into the swarm, creating a powerful trio!

Double-check that all three nodes are indeed part of the team. Type docker node ls to get a list of all active members. You should see something like this:

$ docker node ls
ID                            HOSTNAME            STATUS              AVAILABILITY               MANAGER STATUS
su1bgh1uxqsikf1129tjhg5r8 *   node1               Ready               Active              Leader
t1tgnq38wb0cehsry2pdku10h     node3               Ready               Active              Reachable
wxie5wf65akdug7sfr9uuleui     node2               Ready               Active          

Remember the asterisk by the first node's ID? That means it's our current connection. It's also the leader, with the others ready to step in if needed. Pretty cool, right? Now, time to launch our first app! Let's ship it!

version: '3.1'

services:
    web:
        image: David/docker-swarm-demo-web
        command: gunicorn --bind 0.0.0.0:5000 wsgi:app
        deploy:
            replicas: 2
        secrets:
            - db_password

    nginx:
        image: David/docker-swarm-demo-nginx
        ports:
            - 8000:80
        deploy:
            mode: global

    redis:
        image: redis
        deploy:
            replicas: 1

secrets:
    db_password:
        external: true        

Quickly create a file named docker-compose.yml on your first node.

Use this command to efficiently add the configuration: echo "<your cmd>" > docker-compose.yml

Before deploying, we need to create a secret called db_password as it's referenced in the configuration.

echo "supersecretpassword" | docker secret create db_password -        

Let's instruct Docker to pick up our custom configuration and get things rolling!

docker stack deploy -c docker-compose.yml demo        

After running the command, you'll witness Docker bringing the three services (web, nginx, and redis) to life. Due to naming our stack "demo," their actual names become demo_web, demo_nginx, and demo_redis. To view these active services, use the command "docker service ls". It'll display something like:

$ docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE                                   PORTS
cih6u1t88vx7        demo_web            replicated          2/2                 lsapan/docker-swarm demo-web:latest
u0p1gd6tykvu        demo_nginx          global              3/3                 lsapan/docker-swarm demo-nginx:latest   *:8000->80/
tcp
wa1gz80ker2g        demo_redis          replicated          1/1                 redis:latest        

Images deployed! Containers are spinning up. Wait a bit if replicas aren't ready, Docker might still be downloading.