Developing in Linux Containers

In this article we will show, how you can make use of Linux Containers (LXC) in distributed and heterogeneous development cycles (TL;DR; jump to the Summary).

Motivation

Usually in our development cycle, we edit the sources and run some test and/or builds by using make [ref] before we commit. This cycle is simple and perfect but might fail in some aspects we should not overlook.

The environment in which we run all our development processes matters!

The Makefile and the Python Environment (make install) encapsulate a lot for us, but they do not have access to all prerequisites. For example, there may have dependencies on packages that are installed on the developer’s desktop, but usually are not preinstalled on a server or client system. Another example is; settings have been made to the software on developer’s desktop that would never be set on a production system.

Linux Containers are isolate environments and not to mix up all the prerequisites from various projects on developer’s desktop is always a good choice.

The scripts from Admin’s tooling box can divide in those to install and maintain software:

and the script utils/lxc.sh, with we can scale our installation, maintenance or even development tasks over a stack of isolated containers / what we call the:

SearXNG LXC suite

Hint

If you see any problems with the internet connectivity of your containers read section Internet Connectivity & Docker.

Gentlemen, start your engines!

Before you can start with containers, you need to install and initiate LXD once:

$ snap install lxd
$ lxd init --auto

And you need to clone from origin or if you have your own fork, clone from your fork:

$ cd ~/Downloads
$ git clone https://github.com/searxng/searxng.git searx
$ cd searx

The SearXNG suite consists of several images, see export LXC_SUITE=(... near by git://utils/lxc-searx.env#L19. For this blog post we exercise on a archlinux image. The container of this image is named searx-archlinux. Lets build the container, but be sure that this container does not already exists, so first lets remove possible old one:

$ sudo -H ./utils/lxc.sh remove searx-archlinux
$ sudo -H ./utils/lxc.sh build searx-archlinux

In this container we install all services including searx, morty & filtron in once:

$ sudo -H ./utils/lxc.sh install suite searx-archlinux

To proxy HTTP from filtron and morty in the container to the outside of the container, install nginx into the container. Once for the bot blocker filtron:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  ./utils/filtron.sh nginx install
...
INFO:  got 429 from http://10.174.184.156/searx

and once for the content sanitizer (content proxy morty):

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  ./utils/morty.sh nginx install
...
INFO:  got 200 from http://10.174.184.156/morty/

On your system, the IP of your searx-archlinux container differs from http://10.174.184.156/searx, just open the URL reported in your installation protocol in your WEB browser from the desktop to test the instance from outside of the container.

In such a earXNG suite admins can maintain and access the debug log of the different services quite easy.

In containers, work as usual

Usually you open a root-bash using sudo -H bash. In case of LXC containers open the root-bash in the container using ./utils/lxc.sh cmd searx-archlinux:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux bash
INFO:  [searx-archlinux] bash
[root@searx-archlinux searx]# pwd
/share/searx

The prompt [root@searx-archlinux ...] signals, that you are the root user in the searx-container. To debug the running SearXNG instance use:

$ ./utils/searx.sh inspect service
...
use [CTRL-C] to stop monitoring the log
...

Back in the browser on your desktop open the service http://10.174.184.156/searx and run your application tests while the debug log is shown in the terminal from above. You can stop monitoring using CTRL-C, this also disables the “debug option” in SearXNG’s settings file and restarts the SearXNG uwsgi application. To debug services from filtron and morty analogous use:

$ ./utils/filtron.sh inspect service
$ ./utils/morty.sh inspect service

Another point we have to notice is that each service (SearXNG, filtron and morty) runs under dedicated system user account with the same name (compare Create user). To get a shell from theses accounts, simply call one of the scripts:

$ ./utils/searx.sh shell
$ ./utils/filtron.sh shell
$ ./utils/morty.sh shell

To get in touch, open a shell from the service user (searx@searx-archlinux):

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
./utils/searx.sh shell
// exit with [CTRL-D]
(searx-pyenv) [searx@searx-archlinux ~]$ ...

The prompt [searx@searx-archlinux] signals that you are logged in as system user searx in the searx-archlinux container and the python virtualenv (searx-pyenv) environment is activated.

(searx-pyenv) [searx@searx-archlinux ~]$ pwd
/usr/local/searx

Wrap production into developer suite

In this section we will see how to change the “Fully functional SearXNG suite” from a LXC container (which is quite ready for production) into a developer suite. For this, we have to keep an eye on the Step by step installation:

  • SearXNG setup in: /etc/searx/settings.yml

  • SearXNG user’s home: /usr/local/searx

  • virtualenv in: /usr/local/searx/searx-pyenv

  • SearXNG software in: /usr/local/searx/searx-src

With the use of the utils/searx.sh the SearXNG service was installed as uWSGI application. To maintain this service, we can use systemctl (compare service architectures on distributions).

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  systemctl stop uwsgi@searx

With the command above, we stopped the SearXNG uWSGI-App in the archlinux container.

The uWSGI-App for the archlinux dsitros is configured in git://utils/templates/etc/uwsgi/apps-archlinux/searx.ini, from where at least you should attend the settings of uid, chdir, env and http:

env = SEARX_SETTINGS_PATH=/etc/searx/settings.yml
http = 127.0.0.1:8888

chdir = /usr/local/searx/searx-src/searx
virtualenv = /usr/local/searx/searx-pyenv
pythonpath = /usr/local/searx/searx-src

If you have read the “Good to know section” you remember, that each container shares the root folder of the repository and the command utils/lxc.sh cmd handles relative path names transparent. To wrap the SearXNG installation into a developer one, we simple have to create a smylink to the transparent reposetory from the desktop. Now lets replace the repository at searx-src in the container with the working tree from outside of the container:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  mv /usr/local/searx/searx-src /usr/local/searx/searx-src.old

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  ln -s /share/searx/ /usr/local/searx/searx-src

Now we can develop as usual in the working tree of our desktop system. Every time the software was changed, you have to restart the SearXNG service (in the conatiner):

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  systemctl restart uwsgi@searx

Remember: In containers, work as usual .. here are just some examples from my daily usage:

To inspect the SearXNG instance (already described above):

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  ./utils/searx.sh inspect service

Run Makefile, e.g. to test inside the container:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  make test

To install all prerequisites needed for a Buildhosts:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  ./utils/searx.sh install buildhost

To build the docs on a buildhost Buildhosts:

$ sudo -H ./utils/lxc.sh cmd searx-archlinux \
  make docs.html

Summary

We build up a fully functional SearXNG suite in a archlinux container:

$ sudo -H ./utils/lxc.sh install suite searx-archlinux

To access HTTP from the desktop we installed nginx for the services inside the conatiner:

$ ./utils/filtron.sh nginx install
$ ./utils/morty.sh nginx install

To wrap the suite into a developer one, we created a symbolic link to the repository which is shared transparent from the desktop’s file system into the container :

$ mv /usr/local/searx/searx-src /usr/local/searx/searx-src.old
$ ln -s /share/searx/ /usr/local/searx/searx-src
$ systemctl restart uwsgi@searx

To get information about the searxNG suite in the archlinux container we can use:

$ sudo -H ./utils/lxc.sh show suite searx-archlinux
...
[searx-archlinux]  INFO:  (eth0) filtron:    http://10.174.184.156:4004/ http://10.174.184.156/searx
[searx-archlinux]  INFO:  (eth0) morty:      http://10.174.184.156:3000/
[searx-archlinux]  INFO:  (eth0) docs.live:  http://10.174.184.156:8080/
[searx-archlinux]  INFO:  (eth0) IPv6:       http://[fd42:573b:e0b3:e97e:216:3eff:fea5:9b65]
...