Expert Opinion (Posts about Jenkins)

A Better Way to a Jenkins Service

jmoney — Fri, 13 Dec 2019 22:24:04 GMT

The typical way to install a Jenkins service on a Windows system is to download the JNLP file and then execute the file with Java Web Start^{TM -
Oracle: be quite afraid}. This process manufactures an excess of anxiety and annoyance for the user due to dialog boxes and their controls appearing only upon successful completion of mysterious (magical) events. Upon failure all you can do is puzzle about how ye flask may not be got.

Thanks to me ye need not wonder, for I will show thou how to get ye flask. Executing javaws on the Jenkins JNLP file triggers several actions:

agent.jar is downloaded
WinSW.exe is downloaded
If the JavaWS window appears, the File menu appears within that window, and you click on Install as Windows Service in that menu, WinSW.exe is renamed to the name of the Jenkins service, which is then installed as a proper Windows service
The new service is started using the WinSW.exe as the service executable taking its config from a file generated by Jenkins (agent.jar I'm guessing)
The javaws process is terminated

At first you might reason as I did that since the actual Java command line is configured in the agent config file, that you can just run it directly in a PowerShell script and install that script as a service. However, Windows does not allow services to be defined by script files, only by platform-native executable files. One solution to this problem is represented by the popular NSSM. I find Jenkins's own Windows service wrapper to be much more elegant as it does not use an intermediary process. WinSW merely takes on the name of the service you want to run by executing the command line provided in its config file.

Here is the correct way to automate that whole process (guaranteed to get thou ye flask without any effort):

{%- set agent = {
    'service_name': 'JenkinsAgent',
    'service_long_name': 'Jenkins Agent (powered by WinSW)',
    'service_desc': 'This service runs an agent for Jenkins',
    'service_home': 'C:\\Jenkins',
    'winsw_uri': 'https://github.com/kohsuke/winsw/releases/download/winsw-v2.2.0/WinSW.NET4.exe',
    'winsw_sha512': 'f485dec639155528d804bbeddc69a0d9fe77c44444821a5b6cf557ec0b8f9932153a0411bab0524a47f133d2ee5bf3c03830f32b36c77b83cc7f0b1c5a108b33',
    'jar_sha512': '6lojuezjazurpmarwmzymthvo0aukur9fvgbiro8gdkkbv7t1ps2nhupdixjcqt1uhzqdzjswojkahulfqbeo5fepuc8ordezt5siugmelxncjwnmggmsvepjufomotk',
} %}


# Install {{ agent['service_name'] }}.jar
service-downloaded:
  file.managed:
    - name: {{ agent['service_home'] }}\\{{ agent['service_name'] }}.jar
    - source: https://jenkins.mycorp.com/jnlpJars/agent.jar
    - source_hash: {{ agent['jar_sha512'] }}
    - makedirs: True

# Setup {{ agent['service_name'] }}.xml
service-configured:
  file.managed:
    - name: {{ agent['service_home'] }}\\{{ agent['service_name'] }}.xml
    - contents: |
        <configuration>
          <id>{{ agent['service_name'] }}</id>
          <name>{{ agent['service_long_name'] }}</name>
          <description>{{ agent['service_desc'] }}</description>

          <executable>java.exe</executable>  <!-- Should be AdoptOpenJDK version -->
          <arguments>-Xrs -jar "{{ agent['service_home'] }}\\{{ agent['service_name'] }}.jar" -jnlpUrl https://jenkins.mycorp.com/computer/{{ grains['id'] }}/slave-agent.jnlp -secret {{ pillar[grains['id']]['jnlp_secret_key'] }}</arguments>

          <logmode>rotate</logmode>
          <onfailure action="restart" />
        </configuration>

# Download, install, and start {{ agent['service_name'] }}.exe
service-created:
  file.managed:
    - name: {{ agent['service_home'] }}\\{{ agent['service_name'] }}.exe
    - source: {{ agent['winsw_uri'] }}
    - source_hash: {{ agent['winsw_sha512'] }}
  module.run:
    - service.create:
      - name: {{ agent['service_name'] }}
      - bin_path: {{ agent['service_home'] }}\\{{ agent['service_name'] }}.exe
      - start_type: auto
      - account_name: '.\{{ pillar['robo_account']['name'] }}'
      - account_password: '{{ pillar['robo_account']['pass'] }}'
    - unless:  # Any changes to the data in this state will require a manual service reinstall because the requisite only checks for existence
      - 'if (Get-Service {{ agent['service_name'] }} -ErrorAction SilentlyContinue)
         {
             Write-Error "Do not execute because service {{ agent['service_name'] }} already exists"
         }'
  service.running:
    - name: {{ agent['service_name'] }}
    - enable: True

Visual Studio Power Environment: Jenkins Pipeline Edition

jmoney — Tue, 12 Nov 2019 22:19:59 GMT

Rather than bother with custom groovy to hack the Jenkins declarative pipeline environment, let's use a structural paradigm that has been successful for me because of its simplicity (the only cost being a reusable custom groovy function) and readability (the function wrapper demonstrates what it does in salutary clarity).

int withVSEnvironment(String label, Boolean returnStatus, String script) {
    ret = powershell(
        label: label,
        returnStatus: returnStatus,
        script: """
            foreach (\$_ in cmd /c "`"%VS140COMNTOOLS%`"..\\..\\vc\\bin\\vcvars32.bat > nul 2>&1 & SET") {
                if (\$_ -match '^([^=]+)=(.*)') {
                    [System.Environment]::SetEnvironmentVariable(\$matches[1], \$matches[2])
                }
            }

            $script
        """
    )
    if (returnStatus) {
        return ret
    }
}


pipeline {
    agent any
    stages {
        stage('Stage Left') {
            steps {
                withVSEnvironment(
                    'Building with PowerShell!!!',
                    False,  // returnStatus
                    '''
                    # No weak cmd script here
                    MSBuild.exe Source/Answer/The_Solution.sln /m /t:Clean,Rebuild
                    '''
                )
            }
        }
    }
}

Visual Studio Power Environment

jmoney — Fri, 26 Jul 2019 21:41:13 GMT

It is sometimes interesting to speculate about how unusual feature patterns in Microsoft projects may reflect the traditions or prejudices of the teams involved with creating and evolving those projects. Today's example is "%VS140COMNTOOLS%"..\..\vc\bin\vcvars32.bat, that wily little batch script that mucks your command environment enough to enable most Visual Studio declarative-like thingies to happen (easily) on the command prompt.

So PowerShell has been around for like 17 years now (if you include the Monad proto period). That's enough time for an effective rewrite or two of the Visual Studio codebase and yet we're still stuck with this inconvenient script written in possibly the worst shell still in popular use today. How can we get it to work with possibly the best shell in popular use today? Unfortunately there is no single command that will dump the environment of a cmd subprocess into the parent powershell environment. I found several hacks online proposing to do this, the most correct and elegant being Invoke-Environment.

Note

[Digression] reStructureText's link formatting is egregiously inferior.

What I really wanted was some Groovy code that will dynamically modify the environment of a declarative pipeline with the results of vcvars32.bat. Jenkins pipeline allows for setting environment variables dynamically, but the dynamism packaged into this feature only allows for arbitrary values for a set of a priori variable names. The vcvars32.bat script sets an indeterminate set of variable names. There may still be a way to do this, but my Groovy-fu does not show me how to edit the env object at sufficient introspection.

Here is the essential functionality of Invoke-Environment applied to vcvars32.bat. This is what I used to prime the PowerShell environment for Visual Studio work by pasting the code block directly into the powershell() step before executing Visual Studio commands. This is not the most elegant, but it is only a few more lines than directly sourcing the batch script and seems to be the plainest way to absorb its environment.

foreach ($_ in cmd /c "`"%VS140COMNTOOLS%`"..\\..\\vc\\bin\\vcvars32.bat > nul 2>&1 & SET") {
    if ($_ -match '^([^=]+)=(.*)') {
        [System.Environment]::SetEnvironmentVariable($matches[1], $matches[2])
    }
}

Note

If you are using this in a Jenkins pipeline, all $'s will need to be escaped, \$, to signify that they signal PowerShell variables and not Groovy variables. Also ` is PowerShell's escape character, so `" is an escaped quote.