The Docker container is connected

The Docker container is connected

Earlier, we implemented a network port to access services running within the docker container.

Let's implement connecting to a docker container through a port.

Network port mapping

We created a container for the python app.

w3cschool@w3cschool:~$ docker run -d -P training/webapp python app.py
fce072cc88cee71b1cdceb57c2821d054a4a59f67da6b416fceb5593f059fc6d

In addition, we can specify the network address of the container binding, such as binding 127.0.0.1.

We use the -P parameter to create a container and docker ps to see port 5000 bound host port 32768.

w3cschool@w3cschool:~$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                     NAMES
fce072cc88ce        training/webapp     "python app.py"     4 minutes ago       Up 4 minutes        0.0.0.0:32768->5000/tcp   grave_hopper

We can also use the -p identity to specify that the container port is bound to the host port.

The difference between the two approaches is:

• -P : is a high port that is randomly mapped to the host by the internal port of the container.
• -p : Is the internal port of the container bound to the specified host port.

w3cschool@w3cschool:~$ docker run -d -p 5000:5000 training/webapp python app.py
33e4523d30aaf0258915c368e66e03b49535de0ef20317d3f639d40222ba6bc0

w3cschool@w3cschool:~$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS                     NAMES
33e4523d30aa        training/webapp     "python app.py"     About a minute ago   Up About a minute   0.0.0.0:5000->5000/tcp    berserk_bartik
fce072cc88ce        training/webapp     "python app.py"     8 minutes ago        Up 8 minutes        0.0.0.0:32768->5000/tcp   grave_hopper

In addition, we can specify the network address of the container binding, such as binding 127.0.0.1.

w3cschool@w3cschool:~$ docker run -d -p 127.0.0.1:5001:5002 training/webapp python app.py
95c6ceef88ca3e71eaf303c2833fd6701d8d1b2572b5613b5a932dfdfe8a857c
w3cschool@w3cschool:~$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                                NAMES
95c6ceef88ca        training/webapp     "python app.py"     6 seconds ago       Up 6 seconds        5000/tcp, 127.0.0.1:5001->5002/tcp   adoring_stonebraker
33e4523d30aa        training/webapp     "python app.py"     3 minutes ago       Up 3 minutes        0.0.0.0:5000->5000/tcp               berserk_bartik
fce072cc88ce        training/webapp     "python app.py"     10 minutes ago      Up 10 minutes       0.0.0.0:32768->5000/tcp              grave_hopper

This allows us to access the container's port 5002 by accessing 127.0.0.1:5001.

In the example above, the default is a bound tcp port, and if you want to bind a UPD port, you can add /udp after the port.

w3cschool@w3cschool:~$ docker run -d -p 127.0.0.1:5000:5000/udp training/webapp python app.py
6779686f06f6204579c1d655dd8b2b31e8e809b245a97b2d3a8e35abe9dcd22a
w3cschool@w3cschool:~$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                                NAMES
6779686f06f6        training/webapp     "python app.py"     4 seconds ago       Up 2 seconds        5000/tcp, 127.0.0.1:5000->5000/udp   drunk_visvesvaraya
95c6ceef88ca        training/webapp     "python app.py"     2 minutes ago       Up 2 minutes        5000/tcp, 127.0.0.1:5001->5002/tcp   adoring_stonebraker
33e4523d30aa        training/webapp     "python app.py"     5 minutes ago       Up 5 minutes        0.0.0.0:5000->5000/tcp               berserk_bartik
fce072cc88ce        training/webapp     "python app.py"     12 minutes ago      Up 12 minutes       0.0.0.0:32768->5000/tcp              grave_hopper

The docker port command allows us to quickly see how the port is bound.

w3cschool@w3cschool:~$ docker port adoring_stonebraker 5002
127.0.0.1:5001

Docker container connection

Port mapping is not the only way to connect docker to another container.

Docker has a connection system that allows multiple containers to be connected together to share connection information.

The docker connection creates a parent-child relationship where the parent container can see the information for the child container.

The container is named

When we create a container, docker automatically names it. In addition, we can use the --name identity to name containers, for example:

w3cschool@w3cschool:~$  docker run -d -P --name youj training/webapp python app.py
43780a6eabaaf14e590b6e849235c75f3012995403f97749775e38436db9a441

We can use the docker ps command to view the container name.

w3cschool@w3cschool:~$ docker ps -l
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                     NAMES
43780a6eabaa        training/webapp     "python app.py"     3 minutes ago       Up 3 minutes        0.0.0.0:32769->5000/tcp   youj