Manager and worker nodes in Docker - Step-by-Step Execution

Process Flow - Manager and worker nodes

Start Docker Swarm

↓

Initialize Manager Node

↓

Manager Node Creates Swarm

↓

Worker Nodes Join Swarm

↓

Manager Assigns Tasks

↓

Worker Nodes Execute Tasks

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Manager Monitors and Controls Swarm

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End or Scale Swarm

This flow shows how a manager node initializes a swarm, worker nodes join it, and the manager assigns and monitors tasks.

Execution Sample

Docker

docker swarm init
# On manager node

docker swarm join --token <worker-token> <manager-ip>:2377
# On worker node

Initialize a manager node to create a swarm, then join worker nodes to the swarm using a token.

Process Table

Step	Action	Node Type	Command	Result
1	Initialize swarm	Manager	docker swarm init	Manager node becomes swarm leader
2	Get join token	Manager	docker swarm join-token worker	Displays token for workers
3	Join swarm	Worker	docker swarm join --token <token> <manager-ip>:2377	Worker node joins swarm
4	Assign task	Manager	docker service create --name web nginx	Service created and tasks assigned
5	Run task	Worker	Runs nginx container as task	Worker runs assigned container
6	Monitor swarm	Manager	docker node ls	Shows all nodes and their status
7	Exit	-	-	All nodes active and tasks running

💡 Swarm is running with manager controlling and workers executing tasks

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
Swarm State	Not initialized	Active (manager)	Active (manager + worker)	Active (manager + worker running tasks)	Active (all nodes healthy)
Node Role	None	Manager	Manager + Worker	Manager + Worker	Manager + Worker
Tasks Running	0	0	0	1 (nginx container)	1 (nginx container)

Key Moments - 3 Insights

Why does the worker node need a token to join the swarm?

The token is a secret that the manager generates to securely allow only authorized workers to join. See execution_table step 2 and 3.

Can a worker node become a manager automatically?

No, a worker node joins with the worker role only. Manager nodes are initialized separately. See execution_table step 1 and 3.

What happens if the manager node goes down?

The swarm loses its control plane; tasks may continue but no new tasks or changes can be made until a manager is restored.

Visual Quiz - 3 Questions

Look at the execution table, what command does the worker node run to join the swarm?

A docker swarm init

B docker swarm join --token <token> <manager-ip>:2377

C docker node ls

D docker service create --name web nginx

💡 Hint

Check step 3 in the execution_table for the worker node join command.

At which step does the manager assign tasks to worker nodes?

A Step 4

B Step 2

C Step 5

D Step 6

💡 Hint

Look for the step where a service is created in the execution_table.

What is the swarm state after step 1?

A Not initialized

B Active (worker)

C Active (manager)

D Inactive

💡 Hint

Check variable_tracker for Swarm State after step 1.

Concept Snapshot

Manager node initializes swarm with 'docker swarm init'.
Worker nodes join using a token from manager.
Manager assigns tasks via services.
Workers run tasks assigned.
Manager monitors nodes and controls swarm state.

Full Transcript

In Docker Swarm, the manager node starts the swarm using 'docker swarm init'. This makes it the leader. The manager generates a token that worker nodes use to join the swarm securely. Workers join with 'docker swarm join --token <token> <manager-ip>:2377'. Once joined, the manager can assign tasks by creating services, which workers run as containers. The manager monitors all nodes and manages the swarm's state. If the manager goes down, control is lost until it is restored.