PricingLoginStart free
DevOps Bootcamp · Lesson

Rolling Deploy Behind the Load Balancer

Release with zero downtime in serial.

Lesson 3 of 413 steps

Rolling Deploy Behind the Load Balancer is a free DevOps Bootcamp lesson on CoddyKit. This is lesson 3 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the DevOps Bootcamp learning path, and your progress syncs across the web and the CoddyKit app. The DevOps Bootcamp course includes 4 lessons in total.

Zero Downtime Is the Promise

Update all web nodes without dropping a single request. The trick is a rolling deploy: change a few hosts at a time. 🔄

serial Controls the Batch

Add serial to your play so Ansible works through hosts in small waves instead of all at once.

- hosts: web
  serial: 1
  tasks:
    - import_role:
        name: webapp

Percentages Work Too

serial accepts a percentage or a list of sizes, so you can ramp: a canary first, then larger batches.

serial:
  - 1
  - 25%
  - 50%

Drain Before You Touch

Before updating a node, take it out of rotation. Use delegate_to to tell the load balancer to stop sending it traffic.

- name: Drain node
  community.general.haproxy:
    state: disabled
    host: "{{ inventory_hostname }}"
  delegate_to: lb1

Why delegate_to the LB

The web host cannot disable itself in the balancer; the load balancer must. delegate_to runs that task on lb1 for each web host.

Deploy the New Version

With the node drained, deploy code, render config and let a handler reload the app service for that host only.

- name: Pull release
  ansible.builtin.git:
    repo: "{{ app_repo }}"
    version: "{{ app_version }}"
    dest: /srv/app
  notify: Reload app

Health Check Before Re-Enable

Confirm the node is healthy with uri before sending users back. Never re-add a broken host to the pool.

- name: Wait for health
  ansible.builtin.uri:
    url: http://localhost:8080/health
    status_code: 200
  retries: 5
  delay: 3

Re-Enable in the Balancer

Once healthy, put the node back into rotation, again via delegate_to the load balancer. Traffic flows to the new version.

- name: Enable node
  community.general.haproxy:
    state: enabled
    host: "{{ inventory_hostname }}"
  delegate_to: lb1

max_fail_percentage Guards You

Set max_fail_percentage so the rollout halts if too many hosts fail, stopping a bad release from spreading further.

- hosts: web
  serial: 1
  max_fail_percentage: 20

run_once for Shared Steps

Some steps, like a one-time db migration, should run a single time. Use run_once so only one host executes them.

- name: Migrate db
  ansible.builtin.command: /srv/app/migrate
  run_once: true

The Whole Loop

Per host: drain, deploy, health-check, re-enable. serial repeats that loop in safe waves until the fleet is updated. ✅

Quick Check

One keyword makes the LB step work.

Answer it in the interactive lesson

Recap

You built a rolling deploy: serial batches, drain and re-enable via delegate_to, health checks, and a fail guard. Zero downtime. 🟢

Free to start

Learn DevOps Bootcamp with an AI tutor — free

Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.

Courses
142
Lessons
568
Start learning freeView the full course

Frequently Asked Questions

Is the “Rolling Deploy Behind the Load Balancer” lesson free?

Yes — any 3 lessons of the DevOps Bootcamp learning path, including “Rolling Deploy Behind the Load Balancer”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The DevOps Bootcamp course includes 4 lessons in total.

What will I learn in “Rolling Deploy Behind the Load Balancer”?

Release with zero downtime in serial. You practise DevOps Bootcamp with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start DevOps Bootcamp?

No prior experience is required. DevOps Bootcamp on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “Rolling Deploy Behind the Load Balancer” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this DevOps Bootcamp lesson?

Yes. Every DevOps Bootcamp lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Architect the Project: Roles & Inventory
  2. Provision, Harden & Bootstrap Hosts
  3. Rolling Deploy Behind the Load Balancer
  4. Smoke Tests, Rollback & Notifications
← Back to DevOps Bootcamp