How to create Dotnet Core TeamCity Build Agent on Ubuntu

Setting up a cross platform DevOps environment for ASP.net Core applications, we will learn how to configure a headless ubuntu server to act as TeamCity BuildAgent to use Cake to build ASP.net Core applications.

Important

This guide assumes you have configured a ubuntu headless server with .net core CLI.

Install .net core on ubuntu headless server

Install the prequisites

You will also need install Mono-Complete

Mono is a platform for running and developing applications based on the ecma/iso standards. mono is an open source effort led by xamarin. mono provides a complete clr (common language runtime) including compiler and runtime, which can produce and execute cil (common intermediate language) bytecode (aka assemblies), and a class library.

Mono Project

Install Mono on Ubuntu

Although not strictly necessary to build .net core applications we will also install Mono on the server to facilitate the building of other .net framework applications.

You may need to first add references to the Mono Repository to ensure you get the latest versions.

sudo apt install gnupg ca-certificates
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb https://download.mono-project.com/repo/ubuntu stable-bionic main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
sudo apt update

Install mono-complete via the terminal

sudo apt install mono-complete -y

Test Cake Build on the server

In order to test that we have the server configured correctly We can now try out Cake following instructions from CakeBuild.net - Getting Started example.

Install the Bootstrapper

curl -Lsfo build.sh http://cakebuild.net/download/bootstrapper/linux

Create a Cake script

We will use nano to create the file

nano cake.build

Copy & Paste the sample code

var target = Argument("target", "Default");
 
Task("Default")
  .Does(() =>
{
  Information("Hello World!");
});
 
RunTarget(target);

Information

If you want more information about how to write a cake build script.
Check out How to write a Cake Build script for ASP.net core project

Change permission on build.sh

chmod +x build.sh

Execute the Build

./build.sh

We should see the following result indicating that we were able to successfully build a project using Cake on the server.

Feeds used:
  /home/gary/.nuget/packages/
  https://api.nuget.org/v3/index.json
 
All packages listed in /home/gary/tools/packages.config are already installed.
Analyzing build script...
Processing build script...
Compiling build script...
 
========================================
Default
========================================
Executing task: Default
Hello World!
Finished executing task: Default
 
Task                          Duration            
--------------------------------------------------
Default                       00:00:00.0024922    
--------------------------------------------------
Total:                        00:00:00.0024922

Configure as Build Agent

We are going to be using this server as an external build agent for use with TeamCity. In my scenario I have TeamCity installed on a seperate ubuntu server.

We need to install a few more pre-requisites to enable this.

Install Unzip

sudo apt install unzip

Install Java JDK & JRE

TeamCity is a Java based application therefore all build agents etc have been developed using Java.

Install the default JDK in the ubuntu repository

sudo apt-get install default-jdk

Check your Java Version

 java -version

The version information returned should be similar too

openjdk 11.0.7 2020-04-14
OpenJDK Runtime Environment (build 11.0.7+10-post-Ubuntu-2ubuntu218.04)
OpenJDK 64-Bit Server VM (build 11.0.7+10-post-Ubuntu-2ubuntu218.04, mixed mode, sharing)

Configure JAVA_HOME environment variable
To find out where Java was installed

 sudo update-alternatives --config java

you should see a response similar too

There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-11-openjdk-amd64/bin/java
Nothing to configure.

Copy the path from your preferred installation and then open /etc/environment using nano or another text editor.

sudo nano /etc/environment

At the end of the file on a new line paste the following or whatever your java installation path is

 JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64/bin/java"

Refresh your terminal windows source, to ensure it picks up you change in the current session

 source /etc/environment

We can now test the environment variable has been set

 echo $JAVA_HOME

Create TeamCity User on Server

We are going to create a user on our server which will we use to run the build agent. We will need to create a user with Home Directory, because this is where we are going to install the team city build agent too.

sudo useradd -m netBuild -p S0m*p455W0rD   # use whatever password you want

We also want to create a group for our build agents on the server, we could potentially have several builders running on the server. We create a group to add them all in.

sudo groupadd teamCity

You may also want to give your netBuild account ssh access. So to do this simply edit your ssh config to enable ssh password authentication. Typically we have this set up to only enable ssh keys, but because this user will not have ssh keys defined, we only really want to give it password access and only from computers on our network.

So to do this we will edit our ssh config

sudo nano /etc/ssh/ssh_config

Then simply change the following.

Host *
#   ForwardAgent no
#   ForwardX11 no
#   ForwardX11Trusted yes
   PasswordAuthentication yes
#   HostbasedAuthentication no
#   GSSAPIAuthentication no
#   GSSAPIDelegateCredentials no
#   GSSAPIKeyExchange no
#   GSSAPITrustDNS no
#   BatchMode no
#   CheckHostIP yes
#   AddressFamily any
#   ConnectTimeout 0
#   StrictHostKeyChecking ask
#   IdentityFile ~/.ssh/id_rsa
#   IdentityFile ~/.ssh/id_dsa
#   IdentityFile ~/.ssh/id_ecdsa
#   IdentityFile ~/.ssh/id_ed25519
#   Port 22
#   Protocol 2
#   Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc
#   MACs hmac-md5,hmac-sha1,umac-64@openssh.com
#   EscapeChar ~
#   Tunnel no
#   TunnelDevice any:any
#   PermitLocalCommand no
#   VisualHostKey no
#   ProxyCommand ssh -q -W %h:%p gateway.example.com
#   RekeyLimit 1G 1h
    SendEnv LANG LC_*
    HashKnownHosts yes
    GSSAPIAuthentication yes
    AllowUsers netBuild@192.168.*.*      # You can use any IP Address scheme here, I just chose a common one for demo

Configure using Agent Push from TeamCity

We can now configure this server as BuildAgent from within TeamCity utilizing the Agent Push functionality. Then simply click the install agent, then select Use Custom Setting and select Unix. Then complete the rest of the form with your details.

Set Agent to Auto Start

There are several methods you can use in Linux to set services to auto start when the server reboots.

Using init.d

sudo nano /etc/init.d/buildAgent

Paste the following code, change the name of the USER variable to whatever username required to run the the script. In my case I have created an agentuser account. You may need to change this value to suit your environment.

#!/bin/sh
### BEGIN INIT INFO
# Provides:          TeamCity Build Agent
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Start build agent daemon at boot time
# Description:       Enable service provided by daemon.
### END INIT INFO
#Provide the correct user name:
USER="netBuild"     #  Change Agent user to whatever user will be used to run the process
 
case "$1" in
start)
 su - $USER -c "cd BuildAgent/bin ; ./agent.sh start"
;;
stop)
 su - $USER -c "cd BuildAgent/bin ; ./agent.sh stop"
;;
*)
  echo "usage start/stop"
  exit 1
 ;;
 
esac
 
exit 0

Setting up and Running Additional Build Agents

Provide the sufficient permissions for the file to execute

sudo chmod 755 /etc/init.d/buildAgent

Add it to the start up process

sudo update-rc.d buildAgent defaults

Gary Woodfine

Technical Director at threenine.co.uk

Gary is Technical Director at threenine.co.uk, an independent software vendor specialising in IoT, Field Service and associated managed services,enabling customers to be efficient, productive, secure and scale-able.