コンテナーとしての Go 言語イメージの実行
Prerequisites
Work through the steps to containerize a Go application in Build your Go image.
Overview
In the previous module you created a Dockerfile
for your example application and then you created your Docker image using the command docker build
. Now that you have the image, you can run that image and see if your application is running correctly.
A container is a normal operating system process except that this process is isolated and has its own file system, its own networking, and its own isolated process tree separate from the host.
To run an image inside of a container, you use the docker run
command. It requires one parameter and that's the image name. Start your image and make sure it's running correctly. Run the following command in your terminal.
$ docker run docker-gs-ping
____ __
/ __/___/ / ___
/ _// __/ _ \/ _ \
/___/\__/_//_/\___/ v4.10.2
High performance, minimalist Go web framework
https://echo.labstack.com
____________________________________O/_______
O\
⇨ http server started on [::]:8080
When you run this command, you’ll notice that you weren't returned to the command prompt. This is because your application is a REST server and will run in a loop waiting for incoming requests without returning control back to the OS until you stop the container.
Make a GET request to the server using the curl command.
$ curl http://localhost:8080/
curl: (7) Failed to connect to localhost port 8080: Connection refused
Your curl command failed because the connection to your server was refused. Meaning that you weren't able to connect to localhost on port 8080. This is expected because your container is running in isolation which includes networking. Stop the container and restart with port 8080 published on your local network.
To stop the container, press ctrl-c. This will return you to the terminal prompt.
To publish a port for your container, you’ll use the --publish
flag (-p
for short) on the docker run
command. The format of the --publish
command is [host_port]:[container_port]
. So if you wanted to expose port 8080
inside the container to port 3000
outside the container, you would pass 3000:8080
to the --publish
flag.
Start the container and expose port 8080
to port 8080
on the host.
$ docker run --publish 8080:8080 docker-gs-ping
Now, rerun the curl command.
$ curl http://localhost:8080/
Hello, Docker! <3
Success! You were able to connect to the application running inside of your container on port 8080. Switch back to the terminal where your container is running and you should see the GET
request logged to the console.
Press ctrl-c
to stop the container.
Run in detached mode
This is great so far, but your sample application is a web server and you
shouldn't have to have your terminal connected to the container. Docker can run
your container in detached mode in the background. To do this, you can use the
--detach
or -d
for short. Docker will start your container the same as
before but this time will detach from the container and return you to the
terminal prompt.
$ docker run -d -p 8080:8080 docker-gs-ping
d75e61fcad1e0c0eca69a3f767be6ba28a66625ce4dc42201a8a323e8313c14e
Docker started your container in the background and printed the container ID on the terminal.
Again, make sure that your container is running. Run the same curl
command:
$ curl http://localhost:8080/
Hello, Docker! <3
List containers
Since you ran your container in the background, how do you know if your container is running or what other containers are running on your machine? Well, to see a list of containers running on your machine, run docker ps
. This is similar to how the ps command is used to see a list of processes on a Linux machine.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" 41 seconds ago Up 40 seconds 0.0.0.0:8080->8080/tcp inspiring_ishizaka
The ps
command tells you a bunch of stuff about your running containers. You can see the container ID, the image running inside the container, the command that was used to start the container, when it was created, the status, ports that are exposed, and the names of the container.
You are probably wondering where the name of your container is coming from. Since you didn’t provide a name for the container when you started it, Docker generated a random name. You'll fix this in a minute but first you need to stop the container. To stop the container, run the docker stop
command, passing the container's name or ID.
$ docker stop inspiring_ishizaka
inspiring_ishizaka
Now rerun the docker ps
command to see a list of running containers.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
Stop, start, and name containers
Docker containers can be started, stopped and restarted. When you stop a container, it's not removed but the status is changed to stopped and the process inside of the container is stopped. When you ran the docker ps
command, the default output is to only show running containers. If you pass the --all
or -a
for short, you will see all containers on your system, including stopped containers and running containers.
$ docker ps --all
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" About a minute ago Exited (2) 23 seconds ago inspiring_ishizaka
f65dbbb9a548 docker-gs-ping "/docker-gs-ping" 3 minutes ago Exited (2) 2 minutes ago wizardly_joliot
aade1bf3d330 docker-gs-ping "/docker-gs-ping" 3 minutes ago Exited (2) 3 minutes ago magical_carson
52d5ce3c15f0 docker-gs-ping "/docker-gs-ping" 9 minutes ago Exited (2) 3 minutes ago gifted_mestorf
If you’ve been following along, you should see several containers listed. These are containers that you started and stopped but haven't removed yet.
Restart the container that you have just stopped. Locate the name of the container and replace the name of the container in the following restart
command:
$ docker restart inspiring_ishizaka
Now, list all the containers again using the ps
command:
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
d75e61fcad1e docker-gs-ping "/docker-gs-ping" 2 minutes ago Up 5 seconds 0.0.0.0:8080->8080/tcp inspiring_ishizaka
f65dbbb9a548 docker-gs-ping "/docker-gs-ping" 4 minutes ago Exited (2) 2 minutes ago wizardly_joliot
aade1bf3d330 docker-gs-ping "/docker-gs-ping" 4 minutes ago Exited (2) 4 minutes ago magical_carson
52d5ce3c15f0 docker-gs-ping "/docker-gs-ping" 10 minutes ago Exited (2) 4 minutes ago gifted_mestorf
Notice that the container you just restarted has been started in detached mode and has port 8080
exposed. Also, note that the status of the container is Up X seconds
. When you restart a container, it will be started with the same flags or commands that it was originally started with.
Stop and remove all of your containers and take a look at fixing the random naming issue.
Stop the container you just started. Find the name of your running container and replace the name in the following command with the name of the container on your system:
$ docker stop inspiring_ishizaka
inspiring_ishizaka
Now that all of your containers are stopped, remove them. When a container is removed, it's no longer running nor is it in the stopped state. Instead, the process inside the container is terminated and the metadata for the container is removed.
To remove a container, run the docker rm
command passing the container name. You can pass multiple container names to the command in one command.
Again, make sure you replace the containers names in the following command with the container names from your system:
$ docker rm inspiring_ishizaka wizardly_joliot magical_carson gifted_mestorf
inspiring_ishizaka
wizardly_joliot
magical_carson
gifted_mestorf
Run the docker ps --all
command again to verify that all containers are gone.
Now, address the pesky random name issue. Standard practice is to name your containers for the simple reason that it's easier to identify what's running in the container and what application or service it's associated with. Just like good naming conventions for variables in your code makes it simpler to read. So goes naming your containers.
To name a container, you must pass the --name
flag to the run
command:
$ docker run -d -p 8080:8080 --name rest-server docker-gs-ping
3bbc6a3102ea368c8b966e1878a5ea9b1fc61187afaac1276c41db22e4b7f48f
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3bbc6a3102ea docker-gs-ping "/docker-gs-ping" 25 seconds ago Up 24 seconds 0.0.0.0:8080->8080/tcp rest-server
Now, you can easily identify your container based on the name.
Next steps
In this module, you learned how to run containers and publish ports. You also learned to manage the lifecycle of containers. You then learned the importance of naming your containers so that they're more easily identifiable. In the next module, you’ll learn how to run a database in a container and connect it to your application.