📦 Azure Container Instances (ACI)

📌 Overview

Azure Container Instances (ACI) is the fastest and simplest way to run a container in Azure, without having to manage any virtual machines or adopt a higher-level service like Kubernetes.

• Type: Serverless Containers (PaaS).
• Billing: Per-second billing based on how long the container runs.
• Boot Time: Seconds.

1. Key Concepts

🚀 Serverless

You don't worry about the underlying server. You just say "Here is my Docker Image, run it with 2 CPU and 4 GB RAM." Azure handles the rest.

👥 Container Groups

The top-level resource in ACI is a Container Group.

• Usually contains 1 container.
• Can contain multiple containers (sidecars) that share the same:
  • Lifecycle (start/stop together).
  • Local network (localhost).
  • Storage volumes.

🔄 Restart Policies

• Always: Keep restarting if it crashes (Good for web servers).
• OnFailure: Restart only if it fails (Good for batch jobs).
• Never: Run once and stop (Good for one-off tasks).

3. Serverless Architecture

    USER / SCRIPT             AZURE CLOUD
    =============            =============

   +-------------+          +------------------------+
   |  Run Command|  ----->  | Azure Container Engine |
   | (Az CLI)    |          | (Serverless Management)|
   +-------------+          +------------------------+
                                        |
       (No VM to Manage)                v
                            +------------------------+
                            | [+] MyContainer        |
                            |     (App + Libs)       |
                            |     [ Public IP ]      |
                            +------------------------+

2. Use Cases

1. Event-Driven Applications: Run a script when a file is uploaded to Storage.
2. Data Processing Jobs: Crunch numbers for 10 minutes and then stop.
3. Bursting from AKS: If your Kubernetes cluster is full, you can "burst" extra pods into ACI (Virtual Nodes).
4. Dev/Test: Quickly test a new container image.

3. 🛠️ Hands-on: Create ACI with Azure CLI

Step 1: Create a Container

Run a public Nginx image.

az container create \
  --resource-group myResourceGroup \
  --name myContainer \
  --image nginx \
  --ports 80 \
  --dns-name-label my-unique-app-dns

Step 2: Verify it Works

Get the URL (FQDN) of your container.

az container show \
  --resource-group myResourceGroup \
  --name myContainer \
  --query ipAddress.fqdn \
  --output tsv

Step 3: View Logs

See what's happening inside.

az container logs --resource-group myResourceGroup --name myContainer

Step 4: Delete

az container delete --resource-group myResourceGroup --name myContainer

💡 Exam Tips for AZ-900

• Simplest Way: ACI is the "Simplest" way to run a container.
• No Orchestration: If you need scaling, auto-healing, or complex networking, use AKS. If you just need to run "x", use ACI.
• Per-Second Billing: Great for short-lived tasks.