Docker: Using the host's network

2 min read

If we use the --net=host option with docker to create a new container, it will share it's network namespace with the host machine. It's main advantage is that it will provide higher performance (it will be close to bare metal speed); however, we might get port conflicts.

24/02/2022

How to build a multi architecture container using rootless nerdctl

3 min read

One of the great things about using nerdctl is that it does not try to include everything you might need. This means that if you try to build a container using nerdctl you'll realize you still need to install the buildkit (unless you have installed the "nerdctl-full" version)

Moreover it's something you don't actually need to have installed locally:

$ nerdctl build --help | grep buildkit
Build an image from a Dockerfile. Needs buildkitd to be running.
      --buildkit-host string     BuildKit address [$BUILDKIT_HOST] (default "unix:///run/user/1000/buildkit/buildkitd.sock")

09/02/2022

Running rootless containers with nerdctl

6 min read

It's no secret that docker comes stuffed with many options that many of us don't need. This is why on servers we can find containerd instead of a fully featured docker. Despite that, the real deal breaker is that whatever we are running, we are going to do it with root privileges. We can check this by running the following container:

$ docker run -v /etc:/itc -it --rm alpine sleep 24

And then looking for the process on the host

$ ps auxf

root        1307  0.0  0.1 2084820 46676 ?       Ssl  11:36   0:04 /usr/bin/containerd
root       66978  0.0  0.0 709860  6120 ?        Sl   05:12   0:00  \_ containerd-shim -namespace moby -workdir /var/lib/containerd/io.containerd.runtime.v1.linux/moby/50cf9789d0e68949d1cf79462956bde98b46a4616e8
b81977d8c89d2af9c34e7 -address /run/containerd/containerd.sock -containerd-binary /usr/bin/containerd -runtime-root /var/run/docker/runtime-runc
root       66996  2.0  0.0   1588     4 pts/0    Ss+  05:12   0:00      \_ sleep 24

Is it possible to run rootless containers? Is there an alternative to docker?

08/02/2022

Is it possible to escape from a container on Kubernetes?

3 min read

You might find some documents explaining containers (this applies to docker and Kubernetes as well) as chroot jails on steroids. One might end up thinking it might be as easy to escape from a root container as it is from a root chroot. But that's not true because it's just an analogy.

28/01/2022

Using multi-stage build to optimize Docker images

2 min read

To be able to build a Docker image we might need some packages that we won't be using at runtime, an example of this would be the compiler or any of the tools we might be using to build it (make, ant, maven...)

Instead of installing the tools to remove them later on while building the Docker image we can use a multistage build so we can just copy the artifacts we need to the final image.

17/01/2022