Chapter 20: Jenkins Manual Jobs — Install, Configure and Freestyle

20.5 Configuration: URL, executors, quiet period

By Ravindra Bagale · Last updated: 25 October 2026

Why: the problem

A Jenkins that works on day one can still be wrong for a team. Three settings cause most of the quiet trouble. First, the Jenkins URL: if it says localhost, every email and chat message links to the wrong place, and webhooks from the Git server cannot reach back. Second, executors: each executor runs one build at a time. Too many on a small machine and builds fight for CPU and memory until the server freezes; too few and developers wait in a queue all afternoon. Third, the quiet period: when a developer pushes five commits in one minute, a short wait lets Jenkins build once instead of five times. A Zomato-style team pushing hundreds of times a day saves real hours with these three numbers. There is also the system message, build history limits, and timezone, which matter when people in Pune and London read the same logs. In this lesson you will set all of these in the UI, then write them as Configuration as Code YAML, so the next server gets the same settings without clicks.

What we will build

You will set the Jenkins URL, admin email, system message, executors, quiet period and the user timezone. You will see the queue fill up when executors are too few, and watch the quiet period merge rapid triggers into one build. Then you will install the Configuration as Code plugin, export the current settings, and reload a small jenkins.yaml that sets the same values.

What: every term in plain English

• Jenkins URL — The address Jenkins puts in links, emails and webhook callbacks.
• Executor — A slot that runs one build. A node with 2 executors runs 2 builds at once.
• Build queue — Builds waiting for a free executor.
• Quiet period — Seconds Jenkins waits after a trigger before starting, to merge rapid triggers.
• System message — A banner on the dashboard, for example a maintenance notice.
• JCasC — Jenkins Configuration as Code plugin. Settings in a YAML file.

How: step by step

1. Set the URL and email

   Manage Jenkins > System > Jenkins Location > URL http://localhost:8080/ > System Admin e-mail jenkins@lab.local
   

   What it does: Links in logs and emails are now correct.

   Output

   Saved
   

2. Set the quiet period

   Manage Jenkins > System > Quiet period 10
   

   What it does: Waits 10 seconds after each trigger.

   Output

   Saved
   

3. Set executors

   Manage Jenkins > Nodes > Built-In Node > Configure > Number of executors 2
   

   What it does: Two builds can run at once in the lab.

   Output

   Saved
   

4. Add a system message

   Manage Jenkins > System > System Message: Lab Jenkins - data can be wiped any time
   

   What it does: Visible on the dashboard.

   Output

   Saved
   

5. Set your timezone

   Your name > Account > User Defined Time Zone > Asia/Kolkata
   

   What it does: Build times show in IST for you.

   Output

   Saved
   

6. Install JCasC

   Manage Jenkins > Plugins > Available > Configuration as Code > Install
   

   What it does: Adds Manage Jenkins > Configuration as Code.

   Output

   Success
   

Example 1: See the queue when executors are full

Stack. Jenkins queue, curl

Goal. See the queue when executors are full.

Execute shell box (job slow-job)

echo "start $BUILD_NUMBER on $NODE_NAME executor $EXECUTOR_NUMBER"
sleep 60
echo "done $BUILD_NUMBER"

fill-queue.sh

J=http://localhost:8080
for i in 1 2 3 4; do
  curl -s -X POST -u "ravi:$JENKINS_TOKEN" "$J/job/slow-job/build?delay=0sec" -o /dev/null -w "queued %{http_code}\n"
done
sleep 5
curl -s -u "ravi:$JENKINS_TOKEN" "$J/queue/api/json?tree=items[why]" ; echo

What each line does

• $EXECUTOR_NUMBER — Which executor slot runs this build: 0 or 1 here.
• sleep 60 — Keeps the executor busy.
• ?delay=0sec — Skips the quiet period so the queue fills at once.
• queue/api/json — Shows waiting items and why they wait.

Green output

queued 201
queued 201
queued 201
queued 201
{"_class":"hudson.model.Queue","items":[{"why":"Waiting for next available executor"}]}

Expected result. Two builds run, the rest wait. Jenkins also merges identical queued builds of the same job without parameters, which is why only one waits.

Example 2: Quiet period merges rapid triggers

Stack. curl, quiet period

Goal. Quiet period merges rapid triggers.

rapid.sh

J=http://localhost:8080
before=$(curl -s -u "ravi:$JENKINS_TOKEN" "$J/job/badge-hello/api/json?tree=nextBuildNumber" | sed 's/.*:\([0-9]*\)}/\1/')
for i in 1 2 3 4 5; do
  curl -s -X POST -u "ravi:$JENKINS_TOKEN" "$J/job/badge-hello/build" -o /dev/null
  sleep 1
done
sleep 25
after=$(curl -s -u "ravi:$JENKINS_TOKEN" "$J/job/badge-hello/api/json?tree=nextBuildNumber" | sed 's/.*:\([0-9]*\)}/\1/')
echo "triggers sent: 5, builds made: $((after - before))"

What each line does

• nextBuildNumber — The number the next build will get.
• five POSTs in 5 seconds — Like five quick git pushes.
• quiet period 10 — Each new trigger lands while the first one is still waiting, so they merge.

Green output

triggers sent: 5, builds made: 1

Expected result. One build instead of five. Set quiet period to 0 and run again to see 5 or close to it.

Example 3: The same settings as Configuration as Code

Stack. JCasC plugin, YAML

Goal. The same settings as Configuration as Code.

jenkins.yaml

jenkins:
  systemMessage: "Lab Jenkins - data can be wiped any time"
  numExecutors: 2
  quietPeriod: 10
  securityRealm:
    local:
      allowsSignup: false
unclassified:
  location:
    url: "http://localhost:8080/"
    adminAddress: "jenkins@lab.local"
  timestamper:
    allPipelines: true

apply.sh

docker cp jenkins.yaml jenkins:/var/jenkins_home/jenkins.yaml
curl -s -X POST -u "ravi:$JENKINS_TOKEN" "http://localhost:8080/configuration-as-code/reload" -o /dev/null -w "reload %{http_code}\n"
curl -s -u "ravi:$JENKINS_TOKEN" "http://localhost:8080/api/json?tree=quietPeriod,numExecutors" ; echo

What each line does

• jenkins: / unclassified: — Top-level JCasC sections. Location lives under unclassified.
• allowsSignup: false — Keeps sign-up off even after reload.
• /var/jenkins_home/jenkins.yaml — The default path JCasC reads.
• configuration-as-code/reload — Applies the file without a restart.

Green output

reload 200
{"_class":"hudson.model.Hudson","numExecutors":2,"quietPeriod":10}

Expected result. Settings now live in a file you can review in a merge request.

Verify: did it work?

1. URL is set

   curl -s -u ravi:$JENKINS_TOKEN http://localhost:8080/manage/configure | grep -o "http://localhost:8080/" | head -1
   

   What it does: The URL field has the right value.

   Output

   http://localhost:8080/
   

2. Executors

   curl -s -u ravi:$JENKINS_TOKEN "http://localhost:8080/computer/api/json?tree=totalExecutors"
   

   What it does: Total slots across nodes.

   Output

   {"_class":"hudson.model.ComputerSet","totalExecutors":2}
   

When it is red 1

Jenkins root URL is empty but is required for the proper operation

Cause. The URL was never set.

Fix, step by step

1. Set it in Manage Jenkins > System > Jenkins Location.
2. Or in JCasC under unclassified.location.url.

When it is red 2

Builds stuck: Waiting for next available executor

Cause. All executors busy or 0 executors on the only node.

Fix, step by step

1. Check Manage Jenkins > Nodes.
2. Raise executors in the lab or add an agent.
3. Cancel stuck builds.

When it is red 3

ConfiguratorException: Invalid configuration elements

Cause. A YAML key is wrong or belongs to a plugin not installed.

Fix, step by step

1. Open Manage Jenkins > Configuration as Code > View Configuration to see valid keys.
2. Fix indentation; YAML uses spaces only.

Cleanup

1. Delete slow-job

   java -jar jenkins-cli.jar -s http://localhost:8080 -auth ravi:$JENKINS_TOKEN delete-job slow-job
   

   What it does: Removes the test job.

   Output

   (no output)
   

Practice tasks

Homework: try at home

Recap

• Set the Jenkins URL first.
• Executors limit parallel builds; size them to CPU and RAM.
• Quiet period merges rapid triggers.
• JCasC keeps settings in Git.
• Check settings with the REST API.

FAQ

How many executors per CPU?

A rule of thumb is one per CPU core for heavy builds.

Does quiet period slow developers?

By seconds only, and saves many duplicate builds.

Can JCasC hold secrets?

Only as variables from the environment or a secret store, never plain text.

Why does the queue merge my builds?

Jenkins does not queue two identical builds of the same job without parameters. The second trigger joins the one already waiting. Parameterized builds with different values are kept apart.

Where do I see who changed a setting?

Install the Audit Trail or Job Config History plugin. JCasC in Git gives you history for free through commits.

Interview questions

1. What is Configuration as Code in Jenkins?

   A plugin that applies Jenkins settings from YAML, so servers are reproducible and changes are reviewed.

2. Builds wait a long time in the queue. What do you check?

   Executor count, offline agents, label mismatches, and long-running stuck builds.

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