> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Demo Docker Service
> This guide covers managing Docker services in a Swarm cluster, including creation, scaling, monitoring, and resilience against node failures.
Welcome to this guide on managing Docker services within a Swarm cluster. In this lesson, you'll learn how to create, update, scale, and monitor Docker services. We'll also highlight how running multiple containers as part of a service increases resilience against node failures.
## Verifying the Swarm Cluster
First, ensure your Swarm cluster is properly configured. In this example, our cluster consists of three nodes: one manager (master) node and two worker nodes. Run the following command on the manager node to list all nodes within the cluster:
```bash theme={null}
root@docker-master:/root # docker node ls
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS
qp9scmbhf3cz13rxy342pywc docker-node2 Ready Active Reachable
uildwhelph5pjt6vi197tsn5s docker-master Ready Active Leader
zycf5u8yudke6nfzo74grysx docker-node1 Ready Active Reachable
root@docker-master:/root #
```
## Creating an NGINX Service
Next, create an NGINX service. Because the `--detach=false` flag was not specified, Docker creates the service tasks in the background:
```bash theme={null}
root@docker-master:/root # docker service create nginx
0vehhuvumc1r82u3eijwecl
Since --detach=false was not specified, tasks will be created in the background.
In a future release, --detach=false will become the default.
root@docker-master:/root #
```
Docker automatically assigns a random name to the service if no name is provided.
## Inspecting the Service
After creating the service, list all services to see the assigned name (in this example, "hopeful\_jones"):
```bash theme={null}
root@docker-master:/root # docker service ls
ID NAME MODE REPLICAS
0vehhuvumci0 hopeful_jones replicated 0/1
```
To inspect the tasks of the service, run:
```bash theme={null}
root@docker-master:/root # docker service ps 0v
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE
v3c6kgq7sbwr hopeful_jones.1 nginx:latest docker-node2 Running Running
```
If the container is still pulling the NGINX image from Docker Hub, its state might temporarily display as "Preparing":
```bash theme={null}
root@docker-master:/root # docker service ps 0v
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE
v3c6kgq7sbwr hopeful_jones.1 nginx:latest docker-node2 Running Preparing about a minute ago
root@docker-master:/root #
```
You can further verify that the container is running by checking with the `docker ps` command:
```bash theme={null}
root@docker-master:/root # docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
6c4b985af166 nginx:latest "nginx -g 'daemon …'" 10 seconds ago Up 10 seconds 80/tcp hopeful_jones
```
Each service receives a random name, and each task is suffixed with an incremental identifier (e.g., "hopeful\_jones.1"). The container's name is derived from the task name along with a unique task ID.
## Publishing a Port
Since NGINX serves web content, you might wish to access it via a web browser. To publish a port so that requests on the host are forwarded to the container, update the service as follows. The command below maps port 5000 on the host to port 80 on the NGINX container:
```bash theme={null}
root@docker-master:/root # docker service update --publish-add 5000:80
```
After the update, confirm the published port with:
```bash theme={null}
root@docker-master:/root # docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
0vehhuvumci0 hopeful_jones replicated 1/1 nginx:latest *:5000->80/tcp
```
Now, open a web browser and navigate to the host address at port 5000 to view the NGINX welcome page.
## Removing and Scaling the Service
When you’re done with the service, you can remove it by executing:
```bash theme={null}
root@docker-master:/root # docker service rm 0v
```
After removal, the service list will no longer display any active services.
To demonstrate scaling, recreate a similar service this time with multiple replicas. This showcases how Docker Swarm distributes containers across available nodes for enhanced availability:
```bash theme={null}
root@docker-master:/root # docker service create --replicas 2 --name nginx nginx
Since --detach=false was not specified, tasks will be created in the background.
In a future release, --detach=false will become the default.
root@docker-master:/root #
```
Check the status of the newly created service:
```bash theme={null}
root@docker-master:/root # docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
fuwei5oh8r24 nginx replicated 1/2 nginx:latest
```
Inspect the tasks to see their distribution across nodes:
```bash theme={null}
root@docker-master:/root # docker service ps nginx
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE
0949ij67fe78h nginx.1 nginx:latest docker-master Running Running 29 seconds ago
oyv6thzu1ldt nginx.2 nginx:latest docker-node2 Running Running 19 seconds ago
```
Over time, both replicas should be running and accessible. Initially, one replica might start running before the other is fully up.
## Draining the Manager Node
By default, manager nodes in Docker Swarm can run service tasks. However, if you want the manager node to focus solely on control-plane activities, you can drain it so that no tasks are scheduled on it. Execute the following command on the manager node:
```bash theme={null}
root@docker-master:/root # docker node update --availability drain docker-master
```
Draining the manager node causes any tasks running on it to be shut down and redeployed on other nodes. For example, after draining, the service tasks might appear as follows:
```bash theme={null}
root@docker-master:/root # docker service ps nginx
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
blv43kjwaj7 nginx.1 nginx:latest docker-node1 Running Preparing 5 seconds ago 80/tcp
0949ij67fe78h nginx.1 nginx:latest docker-master Shutdown Shutdown 2 seconds ago 80/tcp
oyw6thzulldt nginx.2 nginx:latest docker-node2 Running Running 3 minutes ago
```
After a short period, Docker Swarm automatically migrates tasks away from the drained manager node.
## Simulating a Node Failure
To demonstrate Docker Swarm’s self-healing capabilities, simulate a node failure by shutting down one of the worker nodes. On docker-node1, run the following command:
```bash theme={null}
root@docker-node1:/root # shutdown now
```
Once the node is shut down, Docker Swarm will automatically redeploy the affected tasks onto the other available nodes—even if this means placing both replicas on a single node. You can check the current status of running containers on the manager node with:
```bash theme={null}
root@docker-master:/root # docker ps
```
This self-healing feature ensures your service remains available even if individual nodes fail.
***
Thank you for reading this guide on managing Docker services in a Swarm cluster. We hope you found the walkthrough helpful. Stay tuned for more advanced topics and best practices in managing containerized applications.