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DevOps Bootcamp · Lesson

Coordinate Web, App & DB Tiers

Sequence a multi-layer rollout.

Lesson 3 of 413 steps

Coordinate Web, App & DB Tiers 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.

Real Apps Have Layers

A typical stack splits into tiers: web servers, app servers and a database. Each tier has its own role and its own deploy order. 🏗️

Order Matters

You usually bring up the database first, then the app, then the web tier. Configuring layers out of order breaks the rollout.

One Play Per Tier

Give each tier its own play in a single playbook. Plays run top to bottom, so their order encodes your deploy sequence.

- hosts: db
  roles: [postgres]

- hosts: app
  roles: [backend]

- hosts: web
  roles: [nginx]

Groups Map to Tiers

Your inventory groups, like db, app and web, line up with the hosts each play targets. The inventory is the backbone of orchestration.

[db]
db01

[app]
app01
app02

[web]
web01
web02

Pass Data Between Tiers

The web tier often needs the app servers' IPs. Read them with hostvars and groups to wire one tier into another.

backends: "{{ groups['app'] | map('extract', hostvars, 'ansible_host') | list }}"

Wait for a Tier to Be Ready

Before the app starts, confirm the database port is open with wait_for. This prevents racing ahead of a slow service.

- ansible.builtin.wait_for:
    host: db01
    port: 5432
    timeout: 60

Run Migrations Once

Database schema changes should fire a single time. Combine run_once with a delegate so one app node migrates the shared DB.

- ansible.builtin.command: ./migrate.sh
  run_once: true
  delegate_to: app01

Reach Across Tiers With delegate_to

An app play can touch the web tier by delegating a task to a web host. One playbook can coordinate every layer.

Tag Tiers for Targeted Runs

Add tags like db, app and web to plays so you can redeploy a single tier with --tags when only one layer changed.

- hosts: web
  tags: web
  roles: [nginx]

Fail Fast Across the Stack

Set any_errors_fatal so a failure in the db tier stops the whole run before the app tier deploys against a broken layer.

- hosts: db
  any_errors_fatal: true
  roles: [postgres]

The Whole Stack, One File

A multi-play playbook becomes your deployment recipe: every tier, in order, with the cross-tier wiring captured in one place.

Quick Check

Let us check how tiers are sequenced.

Answer it in the interactive lesson

Recap

Coordinate tiers with one play per layer in deploy order, wired together via groups, hostvars, wait_for and delegation. ✅

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Frequently Asked Questions

Is the “Coordinate Web, App & DB Tiers” lesson free?

Yes — any 3 lessons of the DevOps Bootcamp learning path, including “Coordinate Web, App & DB Tiers”, 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 “Coordinate Web, App & DB Tiers”?

Sequence a multi-layer rollout. 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 “Coordinate Web, App & DB Tiers” 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. Automating Network Devices with cli_command
  2. delegate_to & run_once for Orchestration
  3. Coordinate Web, App & DB Tiers
  4. Load Balancer Drain & Re-Enable
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