Tuesday, July 11, 2017

Oracle Linux - start a stopped docker container

In our examples we are running a Docker engine on an Oracle Linux host which we use to explain how you can work with Docker and containers. In this example post we do have the need to start a stopped container again. Stopping a container will not remove the container and this means we can start it again if we need to do so. Having the option to stop containers and start them again is a great option especially when you do a rollout of a new version of an application landscape. Building a rollout strategy with a very fast way of rolling back to the original version can be supported by exactly this, the option to stop and start containers. In case your rollout is done correctly you can decide to remove the containers completely, having them around until you decide your rollout is fully complete can be a good practice.

When you execute a standard "docker ps" command you will get only the running containers, in our case we want to see all containers regardless the fact what the state is. For this we need to include the -a flag with the docker ps command as shown in the example below:

[root@localhost log]# docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                        PORTS               NAMES
c1db637d5612        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Exited (143) 30 minutes ago                       nosql_node_3
06fc415798e3        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Exited (143) 33 minutes ago                       nosql_node_2
bf2d698ebcb3        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Exited (143) 30 minutes ago                       nosql_node_1
0a52831c65e8        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Exited (130) 6 minutes ago                        nosql_node_0
[root@localhost log]# 

In case we want to start a container again, in our example we want to start node 0 again we have to use the start command in combination with the container ID. This is shown in the example below:

[root@localhost log]# docker start 0a52831c65e8
0a52831c65e8
[root@localhost log]#

if we now execute a docker ps command (without the -a flag) we will see a list of running containers and we will notice that node 0 of our Oracle NoSQL cluster is back online again and ready to serve requests.

[root@localhost log]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                          NAMES
0a52831c65e8        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up About a minute   5000-5001/tcp, 5010-5020/tcp   nosql_node_0
[root@localhost log]#

As with most commands you can provide multiple container ID's. This means that if we want to start the remaining nodes we can do that with a single command as shown below:

[root@localhost log]# docker start c1db637d5612 06fc415798e3 bf2d698ebcb3
c1db637d5612
06fc415798e3
bf2d698ebcb3
[root@localhost log]#

Checking what is running will show that all four nodes of our Oracle NoSQL cluster are running on our docker engine.

[root@localhost log]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                          NAMES
c1db637d5612        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up 2 seconds        5000-5001/tcp, 5010-5020/tcp   nosql_node_3
06fc415798e3        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up 2 seconds        5000-5001/tcp, 5010-5020/tcp   nosql_node_2
bf2d698ebcb3        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up 2 seconds        5000-5001/tcp, 5010-5020/tcp   nosql_node_1
0a52831c65e8        oracle/nosql        "java -jar lib/kvstor"   11 hours ago        Up About a minute   5000-5001/tcp, 5010-5020/tcp   nosql_node_0
[root@localhost log]# 
Post a Comment