9.7 KiB
| title | keywords | description |
|---|---|---|
| Run your Java image as a container | Java, run, image, container, | Learn how to run the image as a container. |
Prerequisites
Work through the steps to build a Java image in Build your Java image.
Overview
In the previous module, you created your sample application and then you created a Dockerfile that you used to build an image. You created your image using the command docker build. Now that you have an 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 separated from the host.
To run an image inside a container, you use the docker run command. The docker run command requires one parameter which is the name of the image. Start your image and make sure it's running correctly. Run the following command in your terminal:
$ docker run java-docker
After running this command, you’ll notice that you didn't return to the command prompt. This is because your application is a REST server and runs in a loop waiting for incoming requests without returning control back to the OS until you stop the container.
Let’s open a new terminal then make a GET request to the server using the curl command.
$ curl --request GET \
--url http://localhost:8080/actuator/health \
--header 'content-type: application/json'
curl: (7) Failed to connect to localhost port 8080: Connection refused
As you can see, your curl command failed because the connection to your server was refused. It means that you weren't able to connect to the 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 8000 inside the container to port 8080 outside the container, you would pass 8080:8000 to the --publish flag.
Start the container and expose port 8080 to port 8080 on the host.
$ docker run --publish 8080:8080 java-docker
Now, rerun the curl command.
$ curl --request GET \
--url http://localhost:8080/actuator/health \
--header 'content-type: application/json'
{"status":"UP"}
Success! You were able to connect to the application running inside of your container on port 8080.
Now, 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 don't have to be connected to the container. Docker can run your container in detached mode or in the background. To do this, you can use the --detach or -d for short. Docker starts your container as earlier, but this time, it will “detach” from the container and return you to the terminal prompt.
$ docker run -d -p 8080:8080 java-docker
5ff83001608c7b787dbe3885277af018aaac738864d42c4fdf5547369f6ac752
Docker started your container in the background and printed the Container ID on the terminal.
Again, make sure that your container is running. Rerun the curl command.
$ curl --request GET \
--url http://localhost:8080/actuator/health \
--header 'content-type: application/json'
{"status":"UP"}
List containers
As 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, you can run the docker ps command. Just like how you run the ps command in Linux to see a list of processes on your machine, you can run the docker ps command to view a list of containers running on your machine.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5ff83001608c java-docker "./mvnw spring-boot:…" About a minute ago Up About a minute 0.0.0.0:8080->8080/tcp trusting_beaver
The docker ps command provides a bunch of information 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 exposed and the name 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 which does just that, stops the container. You need to pass the name of the container or you can use the container ID.
$ docker stop trusting_beaver
trusting_beaver
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
You can start, stop, and restart Docker containers. When you stop a container, it's not removed, but the status is changed to stopped and the process inside the container is stopped. When you ran the docker ps command in the previous module, the default output only shows running containers. When you pass the --all or -a for short, you see all containers on your machine, irrespective of their start or stop status.
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5ff83001608c java-docker "./mvnw spring-boot:…" 5 minutes ago Exited (143) 18 seconds ago trusting_beaver
630f2872ddf5 java-docker "./mvnw spring-boot:…" 11 minutes ago Exited (1) 8 minutes ago modest_khayyam
a28f9d587d95 java-docker "./mvnw spring-boot:…" 17 minutes ago Exited (1) 11 minutes ago lucid_greider
You should now see several containers listed. These are containers that you started and stopped, but haven't been removed.
Restart the container that you just stopped using the restart command. Find
the name of your container and replace the name in the following command
with the name of the container on your system.
$ docker restart trusting_beaver
Now, list all the containers again using the docker ps command.
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5ff83001608c java-docker "./mvnw spring-boot:…" 10 minutes ago Up 2 seconds 0.0.0.0:8080->8080/tcp trusting_beaver
630f2872ddf5 java-docker "./mvnw spring-boot:…" 16 minutes ago Exited (1) 13 minutes ago modest_khayyam
a28f9d587d95 java-docker "./mvnw spring-boot:…" 22 minutes ago Exited (1) 16 minutes ago lucid_greider
Notice that the container you just restarted has been started in detached mode and has port 8080 exposed. Also, observe the status of the container is “Up X seconds”. When you restart a container, it starts with the same flags or commands that it was originally started with.
Now, stop and remove all of your containers and take a look at fixing the random naming issue. 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 trusting_beaver
trusting_beaver
Now that your container is stopped, remove it. When you remove a container, the process inside the container will be stopped and the metadata for the container will be removed.
To remove a container, simply run the docker rm command passing the container name. You can pass multiple container names to the command using a single command. Again, replace the container names in the following command with the container names from your system.
$ docker rm trusting_beaver modest_khayyam lucid_greider
trusting_beaver
modest_khayyam
lucid_greider
Run the docker ps --all command again to see that all containers are removed.
Now, you can address the random naming issue. The 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.
To name a container, you just need to pass the --name flag to the docker run command.
$ docker run --rm -d -p 8080:8080 --name springboot-server java-docker
2e907c68d1c98be37d2b2c2ac6b16f353c85b3757e549254de68746a94a8a8d3
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
2e907c68d1c9 java-docker "./mvnw spring-boot:…" 8 seconds ago Up 8 seconds 0.0.0.0:8080->8080/tcp springboot-server
That’s better! You can now easily identify your container based on the name.
Next steps
In this module, you took a look at running containers, publishing ports, and running containers in detached mode. You also took a look at managing containers by starting, stopping, and, restarting them. Finally, you looked at naming your containers so 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.
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