Container Orchestration, Load Balancing, Scaling of Containers, Performing rolling Updates, Handling Fail over Scenarios,

Container Orchestration –  

What is Docker container orchestration? 

The Docker container orchestration tool, also known as Docker Swarm, can package and run applications as containers, find existing container images from others, and deploy a container on a laptop, server or cloud (public cloud or private). Docker container orchestration requires one of the simplest configurations. 

This is the process of running docker containers in a distributed environment, on multiple docker host machines. 

All these containers can have a single service running on them and they share the resources between each other, even running on different host machines. 

Docker swarm is the tool used for performing container orchestration 



1) Load balancing 

2) scaling of containers 

3) performing rolling updates 

4) handling failover scenarios 

 Machine on which docker swarm is installed is called as manager. 

Other machines are called as workers. 

Lets create 3 machines 

Name is as Manager, Worker1, Worker2 

All the above machines should have docker installed in it. 

Install docker using 

( Optional step to change the  prompt ) 

After installing docker in the 1st machine ( Manager ),  Lets change the host name. 

Host name will be available in the file hostname. We will change the hostname to manager. 

# vim /etc/hostname 



After changing the hostname, lets restart the machine 

# init 6 


Similary repeat the same in worker1 and worker2 


Connect to Manager, install docker swarm in it. 

$ sudo su – 

Command to install docker swarm  in manager machine 

# docker swarm init –advertise-addr  private_ip_of_manager 

# docker swarm init –advertise-addr 

Please read the log messages 

Now, we need to add workers to manager 

Copy the  docker swarm join command in the log and run in the worker1  and worker2 

Open another gitbash terminal, connect to worker1 

sudo su – 

# docker swarm join –token SWMTKN-1-0etsmfa26vreeytq278q8ohhi73il7j1lpnrzzlowuld1r8yex-9x04pjmiq85jxjzjayzlglh1c 

Repeat for worker2 


TO see the no of nodes from the manager 

Manager # docker  node ls   ( we can see manager, worker1  and worker 2) 


Load balancing: 

Each docker container is designed to withstand a specific  user load. 

When the load increases, we can replica containers in docker swarm and distribute the load. 

Ex: Start tomcat in docker swarm with 5 replicas and name it as webserver. 

Manager# docker service create –name webserver -p 9090:8080 –replicas 5  tomee 

( 5 conainers with the same service, distributed load in 3 machines) 

How to see where thay are running? 

Manager# docker service  ps  webserver 

Lets take the note 

Manager – 1 container 

Worker1 – 2 container 

Worker2 – 2 container 


Note: Only one tomcat is running and load is shrared to 3 machines 

Lets check 

public_ip_manager:9090  ( Will show tomcat page ) 

public_ip_worker1:9090  ( Will show tomcat page ) 

public_ip_worker2:9090  ( Will show tomcat page ) 


Ex 2:  Start mysql in docker swarm with 3 replicas. 

Manager# docker service create –name mydb –replicas 3   -e MYSQL_ROOT_PASSWORD=sunil mysql:5 

How to see where thay are running? 

Manager# docker service  ps  mydb 

To know the total no of services running in docker swarm 

Manager# docker service ls 


If you delete a container, it will create another container. 


Manager# docker service  ps  mydb 

We can see one container is running in  Manager machine 

I want to delete the container which is running in manager 

Manager# docker container ls 

( we can see 1 mysql container, 1 tomcat container ) 

Take note of the container_id  of mysql 


TO delete the container 

# docker rm -f   67238f47bc60 

Now lets check the mydb service 

# docker service  ps  mydb ( we can see one service is failed, automatically 2nd service is started) 

At anypoint of time, 3 container will be running. 


Scaling of containers 

When business requirement increases, we should be able to increase the no of replicas. 

Similarly, we should also be able to decrease the replica count based on business requirement. This scaling should be done without any downtime. 

Ex 3:  Start nginx with 5 replicas, later scale the services to 10. 

# docker service  create  –name appserver -p 8080:80  –replicas 5 nginx 

# docker service ps appserver 

Command to scale 

# docker service scale  appserver=10 

To check 

# docker service ps appserver 

Now I want only two containers 

# docker service scale  appserver=2 

To check 

# docker service ps appserver 


To remove a node from the docker swarm 

Two ways 

1) Manager can drain 

2) Node can leave 

To see the list of nodes 

# docker node ls 

# docker node update –availability drain  Worker1 

All the container running in Worker1 , will be migrated to Worker2 or manager. 

# docker service ps mydb 

# docker node ls 

To add the node 

# docker node update –availability active  Worker1 

# docker node ls 

2nd Way  ( Node can leave ) 


Lets Connect to worker2 from git bash 

Worker2# docker swarm leave 


TO see the list of services 

# docker service ls 

TO delete the services 

Manager# docker service rm appserver mydb webserver 

Rolling Updates 


The services running in docker swarm, can be updated to any other version 

without any downtime.  

This is perfomed by docker swarm by updating one replica after another. This is called as rolling update. 

Ex: Create redis 3 service with 6 replicas. Update from redis 3 to redis 4 version. 

docker service create –name myredis –replicas 6 redis:3 

To check the replicas 

docker service ps myredis 

To update 

# docker service update –image redis:4 myredis 

docker service ps myredis  

I want to display running containers not shutdown containers 

# docker service ps myredis | grep Shutdown  ( We get shutdown container ) 

# docker service ps myredis | grep -v Shutdown ( -v used for inverse operation ) 


Performing rolling rollback , to downgrade to redis:3 version 

# docker service update –rollback myredis 

To check redis:3 is running with 6 replicas and other version are shutdown. 

# docker service ps myredis 


TO add new nodes, in future, we need to docker swarm join command. 

To generate the command 

# docker swarm  join-token  worker  ( We will get the command ) 

docker swarm join –token SWMTKN-1-0etsmfa26vreeytq278q8ohhi73il7j1lpnrzzlowuld1r8yex-9x04pjmiq85jxjzjayzlglh1c 


To add a new machine as a manager 

# docker swarm  join-token  manager 

docker swarm join –token SWMTKN-1-5wbamgr8x7gxabwtlm1j1i91bm5ilzotgna6bc0edubtwtjxi1-3jmzi67qdn5aawvielkcng2e4 


If there are two managers, one will be leader 

# docker node ls   ( we can see who is the leader ) 

Decision of which is machine should be leader is automatic. 

If one manager goes down, other manager automatically become leader. 


To promote worker1 as a manager node 

# docker node promote Worker1 

To demote Worker1 and make him back as a worker 

# docker node demote Worker1 

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