Containers

  1. Programming-level, e.g. Python's Virtualenv
  2. Kernel-level
    1. Application encapsulating:, e.g.Docker (ephemeral, separate storage)
    2. OS encapsulating, e.g. LXC, LXD, and kind-of chroot (UNIX)
  3. Hardware virtualisation
    1. Heavyweight OS (Type 2 hosted hypervisor), e.g. Vagrant (depending on back-end), Virtualbox
    2. (Type 1 bare metal) Hypervisor, e.g. KVM, Hyper-V

Docker, LXC, LXD (uses LXC) all use, on Linux, Linux cgroups and namespaces(net, user, pid, ipc, cgroup).

Kubernetes can be used for orchestration.

You also have things like Firejail, Snap/Flatpak, and AppImage.

Containers may conflate:

  • Security via isolation
  • Packaging dependencies
  • Efficient resource utilisation

Developing with Vagrant

Consider LXD as a lightweight, non-portable alternative.

This is useful if you are working on conflicting projects, or want to keep your computer tidy. Keep your setup on your host (text editor and IDE appliations and their config files), and run the project (any executables) within the container. A shared folder can be used to store the repository.

Vagrant is easy if you use the default Virtualbox provider. And, apparently, impossible with vagrant-lxc :/

Plugins (they have been a disaster for me):

  • vagrant-vbguest to keep VirtualBox's Guest Additions up-to-date on the Vagrant box that started failing
  • vagrant-notify-forwarder for filesystem event forwarding that is not reliable
  • vagrant-disksize to easily increase the size of your Virtualbox disk
    • config.disksize.size = '20GB'
  • vagrant-share to be able to share your container with others that I've never used
  • vagrant-lxc for LXC boxes that don't work

Create a merging custom Vagrantfile in ~/vagrant.d/.

Many applications inside the virtual machine will bind to localhost making them difficult to connect to from the host. We can configure a SOCKS5 proxy with SSH, and use a new profile of Firefox which always connect via that proxy.

config.vm.network "private_network", ip: "172.16.3.2"
config.ssh.extra_args = ["-D", "1632"]

Using the Firefox extension SmartProxy, add the SOCKSv5 Proxy Server (Vagrant; SOCKS5; 127.0.0.1; 1632). Then when browsing to a particular localhost:<port>, click on the toolbar icon and enable "Enable proxy on localhost:<port>".

It is also possible to connect the VM's shared private network directly on 172.16.3.2.

This is easier than forwarding each individual application (which you may not know in advance) with:

config.vm.network "forwarded_port", guest: 8000, host: 8000, host_ip: "127.0.0.1"

Issue with Kubectl

If you encounter an issue with double port-forwarding (i.e. a port-forward inside the guest and then using Vagrant's port-forward to forward it to your host): https://stackoverflow.com/questions/49940964/windows-host-vagrant-kubectl-port-forward-stuck-inside-vagrant. TODO: I have no idea what that is doing ATM.

# Port Forward from local port 8000 to remote port 80, listening on all addresses so that Vagrant's port forwarding works.

kubectl port-forward --address 0.0.0.0 8000:80

Developing with Docker

  • Use tini for your applications to handle signals (article).

https://blog.realkinetic.com/building-minimal-docker-containers-for-python-applications-37d0272c52f3

https://pythonspeed.com/docker/

https://cloud.google.com/solutions/best-practices-for-building-containers

https://cloud.google.com/solutions/best-practices-for-operating-containers

Best Practises

  • Use hadolint, a docker file linter
  • Use tini as the correct init (forwards signals and reaps zombies) (article)

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