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

Most often 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 & ./manage and the Python environment (make install) encapsulate a lot for us, but these tools do not have access to all prerequisites. For example, there may have dependencies on packages that are installed on 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, we use them to not mix up all the prerequisites from various projects on developer’s desktop.

The scripts from DevOps tooling box can divide in those to install and maintain software

and the script

with we can scale our installation, maintenance or even development tasks over a stack of isolated containers / what we call the:

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 searxng
$ cd searxng

The SearXNG suite config consists of several images, see export LXC_SUITE=(... near by git://utils/lxc-searxng.env#L19. For this blog post we exercise on a archlinux image. The container of this image is named searxng-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 searxng-archlinux
$ sudo -H ./utils/lxc.sh build searxng-archlinux

To install the complete SearXNG suite and the HTTP proxy NGINX into the archlinux container run:

$ sudo -H ./utils/lxc.sh install suite searxng-archlinux
$ sudo -H ./utils/lxc.sh cmd -- FORCE_TIMEOUT=0 ./utils/searxng.sh install nginx
$ sudo ./utils/lxc.sh show suite | grep SEARXNG_URL
...
[searxng-archlinux]    SEARXNG_URL          : http://n.n.n.140/searxng

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

In the example above the SearXNG instance in the container is wrapped to http://n.n.n.140/searxng to the HOST system. Note, on your HOST system, the IP of your searxng-archlinux container is different to this example. To test the instance in the container from outside of the container, in your WEB browser on your desktop just open the URL reported in your installation

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 is done by the ./utils/lxc.sh cmd searxng-archlinux command:

$ sudo -H ./utils/lxc.sh cmd searxng-archlinux bash
INFO:  [searxng-archlinux] bash
[root@searxng-archlinux SearXNG]$

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

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

Back in the browser on your desktop open the service http://n.n.n.140/searxng 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.

Another point we have to notice is that the service SearXNG runs under dedicated system user account with the same name (compare Create user). To get a login shell from these accounts, simply call:

$ ./utils/searxng.sh instance cmd bash -l
(searx-pyenv) [searxng@searxng-archlinux ~]$ pwd
/usr/local/searxng

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

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/searxng/settings.yml

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

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

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

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

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

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

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

env = SEARXNG_SETTINGS_PATH=/etc/searxng/settings.yml
http = 127.0.0.1:8888

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

If you have read the Good to know 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 in the container into a developer one, we simple have to create a symlink to the transparent repository from the desktop. Now lets replace the repository at searxng-src in the container with the working tree from outside of the container:

$ mv /usr/local/searxng/searxng-src  /usr/local/searxng/searxng-src.old
$ ln -s /share/SearXNG/ /usr/local/searxng/searxng-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 container):

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

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

To inspect the SearXNG instance (already described above):

$ ./utils/searx.sh inspect service

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

$ make test

To install all prerequisites needed for a Buildhosts:

$ ./utils/searxng.sh install buildhost

To build the docs on a buildhost Buildhosts:

$ make docs.html

Summary

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

$ sudo -H ./utils/lxc.sh build searxng-archlinux
$ sudo -H ./utils/lxc.sh install suite searxng-archlinux
...
Developer install? (wraps source from HOST into the running instance) [YES/no]

To wrap the suite into a developer one answer YES (or press Enter).

link SearXNG's sources to: /share/SearXNG
=========================================

mv -f "/usr/local/searxng/searxng-src" "/usr/local/searxng/searxng-src.backup"
ln -s "/share/SearXNG" "/usr/local/searxng/searxng-src"
ls -ld /usr/local/searxng/searxng-src
  |searxng| lrwxrwxrwx 1 searxng searxng ... /usr/local/searxng/searxng-src -> /share/SearXNG

On code modification the instance has to be restarted (see uWSGI maintenance):

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

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

$ sudo -H ./utils/lxc.sh cmd -- FORCE_TIMEOUT=0 ./utils/searxng.sh install nginx

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

$ sudo -H ./utils/lxc.sh show suite searxng-archlinux
[searxng-archlinux]  INFO:  (eth0) docs-live:  http:///n.n.n.140:8080/
[searxng-archlinux]  INFO:  (eth0) IPv6:       http://[fd42:555b:2af9:e121:216:3eff:fe5b:1744]
[searxng-archlinux]  uWSGI:
[searxng-archlinux]    SEARXNG_UWSGI_SOCKET : /usr/local/searxng/run/socket
[searxng-archlinux]  environment /usr/local/searxng/searxng-src/utils/brand.env:
[searxng-archlinux]    GIT_URL              : https://github.com/searxng/searxng
[searxng-archlinux]    GIT_BRANCH           : master
[searxng-archlinux]    SEARXNG_URL          : http:///n.n.n.140/searxng
[searxng-archlinux]    SEARXNG_PORT         : 8888
[searxng-archlinux]    SEARXNG_BIND_ADDRESS : 127.0.0.1