Docker Swarm

 

Src https://docs.docker.com/engine/swarm/how-swarm-mode-works/nodes/

Docker Swarm:

Docker swarm is a container orchestration clustering tool in simple manages multiple containers that running on the group of the docker host

Benefits of running containers in docker in the swarm mode

àHigh availability of services

àLoad balancing

àScaling the containers

àRolling updates

 

Swarm Architecture:

àOne node will be acting as a Manager Node can add any no of nodes but primary task manages the cluster

àworker node will run actual load

àcontainers will be running in form of services

Creating the docker swarm cluster

àgoing to create a cluster of 3 nodes one is manager, worker1 and worker2 in docker swarm can create any no of manager nodes and any no of worker nodes

àIf you want to add a node as a manager by the command before that you can start docker on all the nodes

Docker swarm init --advertise-addr ipAddress  --it acts as a manager it will start the cluster to add workers to this swarm

It gives the command like token

Docker swarm join \

 --token swatkljsjkas -1-2ashhjkashkalkslksajlkjklasjkljsakfasf \

10.142.2.1:2377

àthis command will run on other nodes it will become worker nodes if you want to retrieve back to the command it means to add worker nodes type docker swarm join-token worker it will give the command use this command as any node to become a worker node

àdocker node ls        --it shows the list of clusters and its status

àIf you want to become a any node as a manager to run this docker swarm join-token manager it gives the command and it run on node to become a manager   

Creating containers in docker swarm cluster:

àcreating container in docker swarm in the form of service by the following command

Docker service create -p 8001:80 --name websvc nginx      --it starts the container from the image nginx and it exposes a port on 8001 and it can access the service on all the worker nodes and manager node also because all are in the same cluster, they are open for

àdocker service ls     --to see the service is running or not

àdocker ps webservice(serviceName)         --it shows the details and where it is running if the load is running on the manager node you can change the load into the worker node by draining the manager node by the command

àdocker node update --availability drain manager to drain no-load take the manager node

àdocker service ps webservice        --to show the service running on the worker node you go to that worker node and give the command docker ps it will show the service running get the ip address followed by the port mapping it will show the service on any of the nodes it may be worker node or manager node because that port is open any for cluster-wide     

àIf you want to do the maintenance of worker 1 it will shut down or drain worker 1 the services are running on the worker 1 is shifted into worker 2 nodes by achieving the High availability of the service

Secalling up the service:

àdocker service scale webservice=10         --it means it increase the resources to 10 to show docker service ls and see where it is running by the docker service ps webservice to show the whare it is running

àdocker node update --availability active manager           --it means the manager node is ready to take the load it is an active state