Episode 18: Docker Swarm – Introduction to Orchestration

[Sascha]

In previous episodes, we explored Docker Compose for managing multi-container applications. Now, it’s time to move into container orchestration — managing multiple containers across different machines. One of the first orchestration tools introduced by Docker itself is Docker Swarm.

What is Docker Swarm?

• Docker Swarm is Docker’s native clustering and orchestration tool.
• It allows you to create a cluster of Docker nodes and deploy services across them.
• Provides high availability, scalability, and load balancing.

Think of it as a way to run containers not just on one machine but across many machines working together.

Key Concepts

1. Node → A machine participating in the swarm (can be physical or virtual).

• Manager Node: Handles cluster management, scheduling, and orchestration.
• Worker Node: Executes the tasks given by the manager.

1. 
   Service → Defines how containers (called tasks) should run in the swarm.
   
   
2. 
   Task → A running container assigned to a node.
   
   
3. 
   Overlay Network → Enables communication between containers running on different machines.
   

Setting Up Docker Swarm

1. Initialize Swarm Mode on the first machine (manager):

docker swarm init --advertise-addr <MANAGER-IP>

1. Join Worker Nodes (command is shown after swarm init):

docker swarm join --token <WORKER-TOKEN> <MANAGER-IP>:2377

1. Verify Nodes in the Swarm:

docker node ls



Deploying a Service in Swarm


Example: Running an nginx service with 3 replicas


docker service create --name my-nginx --replicas 3 -p 8080:80 nginx




Check running services:


docker service ls
docker service ps my-nginx



Scaling a Service


docker service scale my-nginx=5




This will automatically balance containers across the nodes.

Benefits of Docker Swarm

• Easy setup and integration with Docker CLI.
• Provides load balancing out of the box.
• Ensures high availability — if a container fails, Swarm replaces it.
• Secure by default (TLS encrypted communication).

When to Use Docker Swarm?

• Small to medium production clusters.
• When you need simpler orchestration than Kubernetes.
• For teams already invested in Docker and looking for an easy scaling solution.

In the next episode, we’ll dive into Docker Networking Deep Dive (Bridge, Host, Overlay, Macvlan) to understand how containers communicate in different environments.


Question for you: Do you want me to go deeper into Docker Swarm (advanced service deployments, secrets, configs) before we move to networking, or should we continue to networking next?

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