my-docs/Containerization & Orchestration/Docker/Docker-Swarm.md

Docker Swarm Documentation

Manager Count

To ensure the cluster remains functional, the number of manager nodes must be more than 50%. If it falls below 51%, the cluster will become non-operational.

Example: Setting Up Nginx

Workflow: API → Allocator → Dispatcher → Scheduler

Commands

Cluster Initialization and Management

• Create Cluster

  docker swarm init
  

  Initializes a new Docker Swarm cluster.

• Join Cluster

  docker swarm join
  

  Joins a node to an existing Docker Swarm cluster.

• Create Cluster with Specific Interface

  docker swarm init --advertise-addr <ip or interface name>
  

  Initializes a new Docker Swarm cluster, specifying the IP or interface name to advertise.

• Leave Cluster

  docker swarm leave
  

  Removes a node from the Docker Swarm cluster.

• Unlock Locked Manager

  docker swarm unlock
  

  Unlocks a locked manager node in the Docker Swarm cluster.

Node Management

• List Nodes

  docker node ls
  

  Displays information about the nodes in the cluster.

  Example Output:

  docker node ls
  

  ID                            HOSTNAME   STATUS    AVAILABILITY   MANAGER STATUS   ENGINE VERSION
  8yw8jrjeqczaci0qkuy060g09 *   docker-1   Ready     Active         Leader           24.0.5
  v4gvf7xenw0izmxgvhr6hb2rj     docker-2   Ready     Active                          24.0.5
  kd3ujmt1ey3pw6v9189fouxfa     docker-3   Ready     Active         Reachable        24.0.5
  tm1msy58ztcltt36rs1lb76p7     docker-3   Down      Active                          24.0.5
  

• Remove Node

  docker node rm <node-id>
  

  Removes a node from the cluster.

  Example:

  docker node rm tm1msy58ztcltt36rs1lb76p7
  

• Promote Node to Manager

  docker node promote <hostname or ID>
  

  Promotes a worker node to a manager node.

  Example:

  root@docker-1:~# docker node promote v4gvf7xenw0izmxgvhr6hb2rj
  Node v4gvf7xenw0izmxgvhr6hb2rj promoted to a manager in the swarm.
  

Service Management

• Show Task Status on Cluster

  docker node ps
  

  Displays the status of tasks running on nodes in the cluster.

• List Services

  docker service ls
  

  Lists all services running in the cluster.

• Create Service

  docker service create --name <service-name> <image-name>
  

  Creates a new service with the specified name and image.

• Scale Service

  docker service scale <service-name>=<replica-count>
  

  Scales the number of replicas for a service.

  Example:

  docker service scale nginx=5
  

  Scales the nginx service to 5 replicas.

• Inspect Service

  docker service inspect <service-name>
  

  Displays detailed information about a service.

• Create Service with Replicas and Environment Variables

  docker service create --name <service-name> --replicas <replica-count> --env <env-variable> <image-name>
  

  Creates a new service with the specified name, number of replicas, and environment variables.

  Example:

  docker service create --name nginx --replicas 3 --env MY_ENV_VAR=value nginx
  

  Creates an nginx service with 3 replicas and an environment variable MY_ENV_VAR set to value.