Deploying services in Swarm in Docker - Step-by-Step Execution

Process Flow - Deploying services in Swarm

Initialize Docker Swarm

↓

Create Service Definition

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Run 'docker service create'

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Swarm Scheduler Assigns Tasks

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Tasks Run on Worker Nodes

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Service is Running & Scaled

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Monitor & Update Service

This flow shows how a Docker Swarm service is deployed: starting Swarm, creating a service, scheduling tasks, running containers, and managing the service.

Execution Sample

Docker

docker swarm init

docker service create --name webserver -p 80:80 nginx

docker service ls

docker service ps webserver

This code initializes a swarm, deploys an nginx service named 'webserver' exposing port 80, then lists services and their tasks.

Process Table

Step	Command	Action	Result/Output
1	docker swarm init	Initialize swarm mode on manager node	Swarm initialized: current node is now a manager
2	docker service create --name webserver -p 80:80 nginx	Create and deploy 'webserver' service with nginx image	Service webserver created with 1 replica
3	docker service ls	List all running services	ID NAME MODE REPLICAS IMAGE xyz webserver replicated 1/1 nginx
4	docker service ps webserver	Show tasks for 'webserver' service	ID NAME NODE DESIRED STATE CURRENT STATE abc webserver.1 manager Running Running 5 seconds ago
5	docker service scale webserver=3	Scale service to 3 replicas	webserver scaled to 3
6	docker service ps webserver	Show updated tasks	3 tasks listed, all Running on nodes
7	docker service rm webserver	Remove the service	webserver removed
8	-	No service running	No services listed
9	-	End of deployment lifecycle	Deployment stopped

💡 Service removed and no tasks remain, deployment lifecycle ends.

Status Tracker

Variable	Start	After Step 2	After Step 5	After Step 7
Swarm Mode	Disabled	Enabled	Enabled	Enabled
Service 'webserver' Replicas	0	1	3	0
Service Status	None	Created	Scaled	Removed

Key Moments - 3 Insights

Why does the service have only 1 replica after creation?

By default, 'docker service create' deploys 1 replica unless scaled later, as shown in execution_table step 2 and step 5.

What happens when you run 'docker swarm init' on a node?

It enables swarm mode on that node, making it a manager able to deploy services, as seen in execution_table step 1.

How do tasks relate to service replicas?

Each replica corresponds to a task running a container; scaling changes the number of tasks, shown in steps 4 and 6.

Visual Quiz - 3 Questions

Look at the execution table, after which step does the service run 3 replicas?

A Step 2

B Step 5

C Step 3

D Step 7

💡 Hint

Check the 'Service Replicas' variable in variable_tracker after Step 5.

At which step is the swarm mode enabled on the node?

A Step 1

B Step 2

C Step 4

D Step 7

💡 Hint

Look at execution_table step 1 and variable_tracker 'Swarm Mode' variable.

If you remove the service at step 7, what is the number of replicas after that?

A 3

B 1

C 0

D Undefined

💡 Hint

Refer to variable_tracker 'Service Replicas' after Step 7.

Concept Snapshot

Docker Swarm deploys services as tasks running containers.
Use 'docker swarm init' to start swarm mode.
Create services with 'docker service create'.
Scale replicas with 'docker service scale'.
Monitor with 'docker service ls' and 'docker service ps'.
Remove services with 'docker service rm'.

Full Transcript

This visual execution shows how to deploy services in Docker Swarm. First, you initialize swarm mode on a node using 'docker swarm init'. Then, you create a service with 'docker service create', which deploys one replica by default. You can check running services with 'docker service ls' and see their tasks with 'docker service ps'. To increase the number of replicas, use 'docker service scale'. Finally, you can remove the service with 'docker service rm'. Each step changes the swarm state and service replicas, which is tracked in the variable tracker. This helps beginners understand how services run and scale in a swarm cluster.