Some container images include more than one executable file, and you may want to run a container using other than the default command and/or pass some arguments to it. In this challenge, you'll practice running an alternative executable in an off-the-shelf container image.
When invoked without extra arguments, the docker run redis command will start a redis-server binary in a container.
However, the redis image also includes the redis-cli executable,
which can be used to interact with any Redis server instance
(not necessarily the one running in the same container).
This makes a redis container a handy way to run redis-cli without installing it on your machine.
But only if you know how to override its default command 😉
In this challenge, you'll practice using the docker run command with arguments overrides.
Using the --rm flag of the docker run command in this challenge should be avoided.
It's a completely valid approach, but it makes the container removed almost immediately after it exits,
which may cause the solution checks to not notice the correct container (hence, never pass).
To get started, run redis-cli with the --version flag in a redis container:
Hint 1 💡
Docker designed containers in such a way that they can be run without any additional arguments by default.
For instance, docker run redis will start a redis process in a container,
because the redis image has a default redis-server command
defined in its Dockerfile:
FROM ...some base image...
RUN ..install redis...
# Run the redis-server command by default
CMD ["redis-server"]
However, oftentimes container images include more than one executable file, and you may want to run a container using other than the default command and/or pass some arguments to it.
Luckily, the docker run command is flexible enough to support this:
docker run [OPTIONS] IMAGE [COMMAND] [ARG...]
Now, let's connect to a remote Redis server using the containerized redis-cli binary.
The Redis server is reachable at 172.16.0.3:6379, and you can use redis-cli -h <host> to connect to it.
Run the redis-cli -h 172.16.0.3 ping command in a redis container:
Hint 2 💡
If the container is failing to connect to Redis,
make sure you use the -h flag with the right IP address and without the port number.
If you really want to specify the port number, you can use the -p flag for that.
Hint 3 💡
While it wouldn't be a strict requirement in a real-world scenario,
the challenge expects you to run the ping command after connecting to the Redis server.
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