# The problem

docker run -p 8083:8083 myrest-app

docker run --network "host" --name "app" myrest-app

So passing the flag --network with value host will allow you container to access your computer network.

Please ignore my first approach, instead use a better alternative that does not expose the container to the entire host network... is possible to make it work, but is not a best practice.

A Better Alternative

Create a network to be used by both containers:

docker network create external-api

Then run both containers with the flag --network external-api.

docker run --network "external-api" --name "app" -p 8083:8083 myrest-app

and

docker run -d --network "external-api" --name "api" -p 3000:3000 dockerExternalId/external-rest-api

The use of flag -p to publish the ports for the api container are only necessary if you want to access it from your computers browser, otherwise just leave them out, because they aren't needed for 2 containers to communicate in the external-api network.

TIP: docker pull is not necessary, once docker run will try to pull the image if does not found it in your computer. Let me know how it went...

Call the External API

So in both solutions I have added the --name flag so that we can reach the other container in the network.

So to reach the external api from my rest app you need to use the url http://api:3000/externalrestapi/testresource.

Notice how I have replaced localhost by api that matches the value for --name flag in the docker run command for your external api.

From your myrest-app container if you try to access http://localhost:3000/externalrestapi/testresource, it will try to access 3000 port of the same myrest-app container.

Because each container is a separate running Operating System and it has its own network interface, file system, etc.

Docker is all about Isolation.

There are 3 ways by which you can access an API from another container.

1. Instead of localhost, provide the IP address of the external host machine (i.e the IP address of your machine on which docker is running)
2. Create a docker network and attach these two containers. Then you can provide the container_name instead of localhost.
3. Use --link while starting the container (deprecated)