Hetzner build machine

This is part of a series of posts on compiling a custom version of Qt5 in order to develop for both amd64 and a Raspberry Pi.

Building Qt5 takes a long time. The build server I was using had CPUs and RAM, but was very slow on I/O. I was very frustrated by that, and I started evaluating alternatives. I ended up setting up scripts to automatically provision a throwaway cloud server at Hetzner.

Initial setup

I got an API key from my customer's Hetzner account.

I installed hcloud-cli, currently only in testing and unstable:

apt install hcloud-cli

Then I configured hcloud with the API key:

hcloud context create

Spin up

I wrote a quick and dirty script to spin up a new machine, which grew a bit with little tweaks:


# Create the server
hcloud server create --name buildqt --ssh-key … --start-after-create \
                     --type cpx51 --image debian-10 --datacenter …

# Query server IP
IP="$(hcloud server describe buildqt -o json | jq -r .public_net.ipv4.ip)"

# Update ansible host file
echo "buildqt ansible_user=root ansible_host=$IP" > hosts

# Remove old host key
ssh-keygen -f ~/.ssh/known_hosts -R "$IP"

# Update login script
echo "#!/bin/sh" > login
echo "ssh root@$IP" >> login
chmod 0755 login

I picked a datacenter in the same location as where we have other servers, to get quicker data transfers.

I like that CLI tools have JSON output that I can cleanly pick at with jq. Sadly, my ISP doesn't do IPv6 yet.

Since the server just got regenerated, I remove a possibly cached host key.

Provisioning the machine

One git server I need is behind HTTP authentication. Here's a quick hack to pass the relevant .netrc credentials to ansible before provisioning:


import subprocess
import netrc
import tempfile
import json

login, account, password = netrc.netrc().authenticators("…")

with tempfile.NamedTemporaryFile(mode="wt", suffix=".json") as fd:
        "repo_user": login,
        "repo_password": password,
    }, fd)

        "-i", "hosts",
        "-l", "buildqt",
        "--extra-vars", f"@{fd.name}",
        ], check=True)

And here's the ansible playbook:

#!/usr/bin/env ansible-playbook

- name: Install and configure buildqt
  hosts: all
   - name: Update apt cache
        update_cache: yes
        cache_valid_time: 86400

   - name: Create build user
        name: build
        comment: QT5 Build User
        shell: /bin/bash

   - name: Create sources directory
     become: yes
     become_user: build
        path: ~/sources
        state: directory
        mode: 0755

   - name: Download sources
     become: yes
     become_user: build
        url: "https://…/{{item}}"
        dest: "~/sources/{{item}}"
        mode: 0644
      - "qt-everywhere-src-5.15.1.tar.xz"
      - "qt-creator-enterprise-src-4.13.2.tar.gz"

   - name: Populate home directory
     become: yes
     become_user: build
        src: build
        dest: ~/
        mode: preserve

   - name: Write .netrc
     become: yes
     become_user: build
        dest: ~/.netrc
        mode: 0600
        content: |
           machine …
           login {{repo_user}}
           password {{repo_password}}

   - name: Write .screenrc
     become: yes
     become_user: build
        dest: ~/.screenrc
        mode: 0644
        content: |
           hardstatus alwayslastline
           hardstatus string '%{= cw}%-Lw%{= KW}%50>%n%f* %t%{= cw}%+Lw%< %{= kK}%-=%D %Y-%m-%d %c%{-}'
           startup_message off
           defutf8 on
           defscrollback 10240

   - name: Install base packages
        name: git,mc,ncdu,neovim,eatmydata,devscripts,equivs,screen
        state: present

   - name: Clone git repo
     become: yes
     become_user: build
        repo: https://…@…/….git
        dest: ~/…

   - name: Copy Qt license
     become: yes
     become_user: build
        src: qt-license.txt
        dest: ~/.qt-license
        mode: 0600

Now everything is ready for a 16 core, 32Gb ram build on SSD storage.

Tear down

When done:

hcloud server delete buildqt

The whole spin up plus provisioning takes around a minute, so I can do it when I start a work day, and take it down at the end. The build machine wasn't that expensive to begin with, and this way it will even be billed by the hour.

A first try on a CPX51 machine has just built the full Qt5 Everywhere Enterprise including QtWebEngine and all its frills, for amd64, in under 1 hour and 40 minutes.