Obtaining the ip address of a docker container

Question

I have a ubuntu machine which is a VM where I have installed docker in it. I am using this machine from my local windows machine and doing ssh , opening the terminal to the ubuntu machine.

Now , I am going to take a docker image which contains all the necessary softwares for eg: apache installed in it. Later I am going to deploy a sample appication(which is a web applicationP on to it and save it .

Now , I am in a confused mode as in how to check the deployed application if its running properly. i.e., what would be the address of the container which containds the deployed application. for eg:- If I type http://127.x.x.x which is the address of the ubuntu machine , I am just getting time out .

Can anyone tell me how to verify the deployed application . Also, the printing the output of the program on the console works seemlessly fine , as the output gets printed , only thing I have some doubts is regarding the web application.

Answer 1

There are some possibilities to check whether your app is running.

Remote API

As JimiDini said, one possibility is the Docker remote API. You can use it to see all running containers (which would be your use case, right?), inspect a certain container or start and stop containers. The API is a REST-API with several binding for programming languages (at https://docs.docker.io/reference/api/remote_api_client_libraries/). Some of them are very outdated. To use the Docker remote API from another machine, I needed to open it explicitly:

docker -H tcp://0.0.0.0:4243 -H unix:///var/run/docker.sock -d &

Note that the API is open to the world now! In a real scenario you would need to secure it in some way (e.g. see the example at http://java.dzone.com/articles/securing-docker%E2%80%99s-remote-api).

Docker PS

To see all running containers run docker ps on your host. This will list all running containers. If you do not see your app, it is not running. It also shows you the ports your app is exposing. You can also do this via the remote API.

Logs

You can also check the logs. You can run docker attach <container id> to attach to a certain container an see its stdout. You can run also run docker logs <container id> to receive the Docker logs. What I prefer is to write the logs to a certain directory, e.g. all logs to /var/log and mount this folder to my host machine. Then all your logs will end up in /home/ubuntu/docker-logs on your host.

docker run -p 80:8080 -v /home/ubuntu/docker-logs:/var/log:rw my/application

One word to ports and IP

Every container will get its own IP address. You can check this IP address via the remote API or via Docker on the host machine directly. You can also specify a certain host name for the container (by passing the --hostname="test42" to the run command). However, you mostly did not need that.

To access the application in the container, you need to open the port in the container and bind to a port on the host.

In your Dockerfile you need to EXPOSE the port your app runs on:

FROM ubuntu
...
EXPOSE 8080
CMD run-my-app.sh

When you start your container, you need to bind this port to a port of the host:

docker run -p 80:8080 my/application

Now you can access your app on http://localhost:80 or http://127.0.0.1:80.

If you app does not response, check if the container is running by typing docker ps or the remote API. If it is not running, check the logs for the reason.

(Note: If you run your Ubuntu VM in something like VirtualBox and you try to access it from your Windows machine, make sure you opened the ports in VirtualBox too!).

Answer 2

Docker container has a separate IP address. By default it is private (accessible only from the host-machine).

Docker provides all metadata (including IP address) via its API:

1. https://docs.docker.io/reference/api/docker_remote_api_v1.10/#inspect-a-container
2. https://docs.docker.io/reference/api/docker_remote_api_v1.10/#monitor-docker-s-events

You can also take a look at a little tool called docker-gen for inspiration. It monitors docker-events and created configuration-files on host machine using templates.