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I have one Java based application(Jboss version 6.1 Community) with heavy traffic on it. Now I want to migrate this application deployments using docker and docker-swarm for clustering.

Scenario

My application needs two ports exposed from docker container one is web port(i.e.9080) and another one is databases connection port(i.e.1521) and there are few things like logs directory for each container mounted on host system.

Simple Docker example 

docker run -it -d --name web1 -h "My Hostname" -p 9080:9080 -p 1521:1521 -v /home/web1/log:/opt/web1/jboss/server/log/ -v /home/web1/license:/opt/web1/jboss/server/license/ MYIMAGE

Docker with Swarm example

docker service create --name jboss_service --mount type=bind,source=/home/web1/license,destination=/opt/web1/jboss/server/license/ --mount type=bind,source=/home/web1/log,destination=/opt/web1/jboss/server/log/ MYIMAGE

Now if I scale/replicate above service to 2 or 3, which host port it will bind and which mount directory will it bind for the newly created containers ??

Can anyone help me to get how scale and replication service will work in this type of scenario ?

I also gone through --publish and --name global but nothing help me in my case.

Thank you!

chintan thakar
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2 Answers2

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Supporting stateful containers is still immature in the Docker universe. I'm not sure this is possible with Docker Swarm (if it is I'd like to know) and it's not a simple problem to solve.

I would suggest you review the Statefulset feature that comes in the latest version of Kubernetes:

It supports the creation of a unique volume for each container in a scale-up event. As for port handling that is part of Kubernetes nornal Service feature that implements container load balancing.

Mark O'Connor
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I would suggest building your stack into a docker-compose v3 file, which could be run onto an swarn-cluster. Instead publishing those ports, you should expose them. That means, the ports are NOT available onto the hostsystem directly, but in the docker-network. Every Composefile got it's own network by default, eg: 172.18.0.0/24. Each Container got's an own ip and makes that Service available other the specified port. If you scale up to 3 Containers you will got: 172.18.0.1:9080,1521 172.18.0.2:9080,1521 172.18.0.3:9080,1521

You would need a Loadbalancer to access those Services. I do use Jwilder/Nginx if you prefer a container approach. I also can recommand Rancher which comes with an internal Loadbalancer.

In Swarm-mode you have to use the overlay network driver and create the network, otherwise it would just be accessible from the local host itself.

Related to logging, you should redirect your log file to stdout and catch them with an logging driver (fluentd, syslog, graylog2)

For persistent Storage you should have a look at flocker! However Databases might not support those storage implementations. EG: MYsql doesnot support them, mongodb does work with a flocker volume.

It seems like you have to read alot.. :) https://docs.docker.com/

Berndinox
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