Docker Container Connection

We have previously implemented accessing services running in docker containers through network ports.

Some network applications can run in the container. To allow external access to these applications, you can do so by -P or -p parameter to specify port mapping.

Next, we will implement connecting to a docker container through a port.

Network port mapping

We created a container for a python application.

w3codebox@w3codebox:~$ docker run　-d　-P training/webapp python app.py
fce072cc88cee71b1cdceb57c2821d054a4a59f67da6b416fceb5593f059fc6d

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

We use -P Parameter to create a container, using docker ps As can be seen from the container port 5000 Binding host port 32768.

w3codebox@w3codebox:~$ docker ps
CONTAINER ID	IMAGE						COMMAND	...	...	...	PORTS	...	...	...	NAMES
fce072cc88ce	training/webapp		"python app.py"		...		0.0.0.0:32768->5000/tcp	grave_hopper

We can also use -p Identify to specify the container port binding to the host port.

The difference between the two methods is:

• -P :is the container internal portRandommapped to the high port on the host.

• -p : is the container internal port bound toSpecifyto the host port.

w3codebox@w3codebox:~$ docker run　-d　-p　5000:5000 training/webapp python app.py
33e4523d30aaf0258915c368e66e03b49535de0ef20317d3f639d40222ba6bc0

w3codebox@w3codebox:~$ docker ps
CONTAINER ID		IMAGE						COMMAND						...		PORTS												NAMES
33e4523d30aa　　　　　　　　training/webapp		"python app.py"		...		0.0.0.0:5000->5000/tcp	berserk_bartik
fce072cc88ce　　　　　　　　training/webapp		"python app.py"		...		0.0.0.0:32768->5000/tcp	grave_hopper

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

w3codebox@w3codebox:~$ docker run　-d　-p　127.0.0.1:5001:5000 training/webapp python app.py
95c6ceef88ca3e71eaf303c2833fd6701d8d1b2572b5613b5a932dfdfe8a857c
w3codebox@w3codebox:~$ docker ps
CONTAINER ID		IMAGE						COMMAND						...		PORTS													NAMES
95c6ceef88ca　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　5000/tcp,　127.0.0.1:5001->5000/tcp　adoring_stonebraker
33e4523d30aa　　　　　　　　training/webapp		"python app.py"		...		0.0.0.0:5000->5000/tcp　　　　　　　　　　　　　　　berserk_bartik
fce072cc88ce　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　　0.0.0.0:32768->5000/tcp　　　　　　　　　　　　　grave_hopper

This way, we can access 127.0.0.1:5001 to access the container 5000 port.

In the above example, the default is to bind the TCP port. If you want to bind the UDP port, you can add it after the port number. /udp.

w3codebox@w3codebox:~$ docker run　-d　-p　127.0.0.1:5000:5000/udp training/webapp python app.py
6779686f06f6204579c1d655dd8b2b31e8e809b245a97b2d3a8e35abe9dcd22a
w3codebox@w3codebox:~$ docker ps
CONTAINER ID　　　　　　　IMAGE　　　　　　　　　　　　　　　COMMAND　　　　　　　　　　　...　　　PORTS　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　NAMES
6779686f06f6　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　　5000/tcp,　127.0.0.1:5000->5000/udp　drunk_visvesvaraya
95c6ceef88ca　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　　　5000/tcp,　127.0.0.1:5001->5000/tcp　adoring_stonebraker
33e4523d30aa　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　　　　0.0.0.0:5000->5000/tcp　　　　　　　　　　　　　　　berserk_bartik
fce072cc88ce　　　　　　　　training/webapp　　　　　"python app.py"　　　...　　　0.0.0.0:32768->5000/tcp　　　　　　　　　　　　　grave_hopper

docker port Command allows us to quickly view the port binding status.

w3codebox@w3codebox:~$ docker port adoring_stonebraker　5000
127.0.0.1:5001

Docker Container Interconnection

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, sharing connection information.

docker connection will create a parent-child relationship, where the parent container can see the information of the child container.

Container Naming

When we create a container, docker will automatically name it. In addition, we can also use --name Identifier to name the container, for example:

w3codebox@w3codebox:~$ docker run　-d　-P　--name w3codebox training/webapp python app.py
43780a6eabaaf14e590b6e849235c75f3012995403f97749775e38436db9a441

We can use docker ps Command to view container names.

w3codebox@w3codebox:~$ docker ps　-l
CONTAINER　ID　　　　　IMAGE　　　　　　　　　　　　COMMAND　　　　　　　　　　　...　　　　PORTS　　　　　　　　　　　　　　　　　　　　　NAMES
43780a6eabaa　　　　　training/webapp　　　"python　app.py"　　...　　　　　0.0.0.0:32769->5000/tcp　　　w3codebox

New network

First, let's create a new Docker network.

$　docker　network　create　-d　bridge　test-net

Parameter Description:

-dThe parameter specifies the Docker network type, which has bridge and overlay.

Among them, the overlay network type is used for Swarm mode, which can be ignored in this section.

Connect container

Run a container and connect to the newly created test-net network:

$ docker run　-itd　--name　test1　--network　test-net　ubuntu　/bin/bash

Open a new terminal and run another container and add it to test-net network:

$ docker run　-itd　--name　test2　--network　test-net　ubuntu　/bin/bash

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Below, we use ping to prove that test1 Container and test2 The container has established an interconnection.

If test1、test2 If there is no ping command in the container, execute the following command to install ping (instant learning: you can install it in one container, commit the container to an image, and then run the above two containers with the new image).

apt-get　update
apt　install　iputils-ping

In test1 The container can enter the following command:

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Similarly in test2 The container will also successfully connect to:

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So, test1 Container and test2 The container has established an interconnection.

If you have multiple containers that need to connect to each other, it is recommended to use Docker Compose, which will be introduced later.

Configure DNS

We can configure DNS on the host machine /etc/docker/Add the following content to the daemon.json file to set the DNS for all containers:

{
　　"dns"　:　[
　　　　"114.114.114.114",
　　　　"8.8.8.8"
　　]
}

After setting, the DNS of the container will be automatically configured as 114.114.114.114 and 8.8.8.8.

After the configuration is complete, you need to restart docker for it to take effect.

You can use the following command to check if the container's DNS is effective, which will output the container's DNS information:

$ docker run　-it　--rm　　ubuntu　　cat　etc/resolv.conf

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Manually specify the container's configuration

If you only want to set DNS in the specified container, you can use the following command:

$ docker run　-it　--rm　-h　host_ubuntu　　--dns=114.114.114.114　--dns-search=test.com　ubuntu

Parameter Description:

--rm: Automatically clean up the container's file system when the container exits.

-h HOSTNAME or --hostname=HOSTNAME: Set the container's hostname, which will be written to the container's /etc/hostname and /etc/hosts.

--dns=IP_ADDRESS: Add DNS server to the container's /etc/in resolv.conf, let the container use this server to resolve all domains not in /etc/in the hosts.

--dns-search=DOMAIN: Set the container's search domain. When the search domain is set to .example.com, when searching for a host named host, DNS will not only search host but also host.example.com.

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If no DNS is specified when the container starts --dns and --dns-search, Docker will use the host machine's /etc/Configure the container's DNS using resolv.conf.