Deploying Services in Swarm
1. Creating Services
| Option | Values | Description |
|---|---|---|
| docker service create | docker service create [OPTIONS] IMAGE [COMMAND] [ARG...] |
Creates a new service from an image |
| --name | service-name |
Name of the service to be created |
| --replicas | 3 |
Number of tasks (containers) to run |
| --port | 80:80 |
Map host port to container port (host:container) |
| --network | my-network |
Network to connect the service to |
| --env | ENV=value |
Set environment variables in the service |
Example: Creating a Web Service
docker service create --name web-server --replicas 3 --port 80:80 nginx
Example: Creating a Service with Environment Variables
docker service create --name api-server --env NODE_ENV=production --replicas 2 node:18 app.js
2. Listing Services
| Command | Description | Options |
|---|---|---|
| docker service ls | List all services in the swarm | --format to format output, --filter to filter results |
| docker service ls --format json | Display services in JSON format | Useful for scripting and parsing |
| docker service ls --filter name=service_name | Filter services by name | Matches services with the specified name prefix |
3. Inspecting Services
| Property | Description | Example |
|---|---|---|
| docker service inspect <service-name> | Displays detailed information about a service | docker service inspect my-web-service |
| docker service inspect --format | Formats the output using a Go template | docker service inspect --format "{{.ID}}" my-web-service |
Example: Formatting Service Inspection Output
docker service inspect --format "{{.ID}}: {{.Spec.Name}}" my-web-service
4. Listing Service Tasks
| Command | Description | Options | Example |
|---|---|---|---|
| docker service tasks | List tasks for a service | --filter, --format, --no-trunc |
docker service tasks myservice |
Example: Formatting task output as JSON
docker service tasks --format "{{.ID}} - {{.Status.State}}" myservice5. Viewing Service Logs
| Command | Description | Options |
|---|---|---|
| docker service logs | View logs for a service | --details, --follow, --since, --tail, --timestamps |
6. Configuring Replicas
| Option | Values | Description |
|---|---|---|
| --replicas | integer |
Number of service replicas to run |
| --replicas-max | integer |
Maximum number of replicas to scale up to |
Note: The
--replicas flag sets the initial number of service instances (replicas) to run. These replicas are distributed across the swarm nodes.
Warning: If a service is configured with
--replicas 0, it will be stopped but not removed. Use docker service rm to fully remove it.
7. Scaling Services
| Command | Description | Example |
|---|---|---|
| docker service scale | Scales the number of tasks (containers) for a service | docker service scale myapp_web=5 |
Note: Scaling a service to zero stops all tasks but keeps the service definition.
Scaling Service Workflow
- Use
docker service scale <service>=<replicas> - Replicas can be increased or decreased
- Service tasks are automatically distributed across nodes
8. Updating Services
| Option | Values | Description |
|---|---|---|
| docker service update | --image |
Update the service image to a new version |
| docker service update | --replicas |
Change the number of running tasks |
| docker service update | --env |
Update environment variables for the service |
| docker service update | --limit |
Update resource limits (CPU, memory) |
| docker service update | --restart-condition |
Update restart policy for tasks |
Note: Updates are applied gradually to maintain service availability.
Warning: Ensure new image versions are compatible with existing configurations.
9. Setting Update Parallelism
| Option | Values | Description |
|---|---|---|
| --update-parallelism | 0 or 1 |
Number of tasks to update simultaneously. Set to 0 for unlimited parallelism. |
| --update-delay | 0s or time duration |
Delay between updates of tasks. Default is 0s. |
| --update-order | stop-first or start-first |
Determines the order in which tasks are updated. Default is stop-first. |
Example: Update Parallelism in Service Deployment
docker service create \
--name myapp \
--update-parallelism 2 \
--update-delay 10s \
--update-order start-first \
nginx:latest
Note: Setting
--update-parallelism to 0 means all tasks will be updated simultaneously, which can lead to downtime if not handled carefully.
10. Rolling Back Services
| Option | Values | Description |
|---|---|---|
| docker service rollback | service-name |
Rolls back a service to its previous version |
Note: The rollback operation reverts the service to the last known good configuration. If no previous version exists, it will fail.
11. Configuring Placement Constraints
| Constraint | Description | Example |
|---|---|---|
| node.labels | Matches nodes with specific labels | node.labels.environment == production |
| node.id | Matches nodes by ID | node.id == abc123 |
| node.hostname | Matches nodes by hostname | node.hostname != worker1 |
| node.role | Matches nodes by role (manager/worker) | node.role == manager |
| node.platform.os | Matches nodes by OS type | node.platform.os == linux |
| node.platform.arch | Matches nodes by architecture | node.platform.arch == x86_64 |
Example: Deploying Service with Placement Constraints
docker service create \
--name web-app \
--constraint 'node.labels.environment == production' \
--constraint 'node.platform.os == linux' \
nginx:latest
Note: Placement constraints are evaluated at service creation time and can be updated later using
docker service update.
12. Removing Services
| Option | Values | Description |
|---|---|---|
| docker service rm | <service_name> |
Removes one or more services by name |
| docker service rm --force | <service_name> |
Force removal even if service is running |
Note: Removing a service does not remove the underlying images or data volumes unless explicitly configured to do so.