Azure Container Instances (ACI) provides lightweight container execution without orchestration layers, making it ideal for:

• Quick task execution (batch jobs, build agents)
• Temporary workloads requiring fast startup
• Simple container deployments with no scaling needs

Azure Container Apps (ACA) builds on Kubernetes abstractions with these enterprise features:

// Example ACA scaling configuration
{
  "scale": {
    "minReplicas": 1,
    "maxReplicas": 10,
    "rules": [
      {
        "name": "http-rule",
        "custom": {
          "type": "http",
          "metadata": {
            "concurrentRequests": "100"
          }
        }
      }
    ]
  }
}

ACI offers basic networking with:

• Public IP assignment
• VNET integration (premium tier)
• No built-in service discovery

ACA provides advanced networking capabilities:

# Example ACA ingress configuration
ingress:
  external: true
  targetPort: 80
  traffic:
    - latestRevision: true
      weight: 100
  allowInsecure: false

ACI scaling is manual through ARM templates or CLI:

az container create --resource-group myGroup \
  --name myContainer --image myImage \
  --cpu 1 --memory 1.5

ACA supports multiple auto-scaling triggers:

// KEDA scaler example for ACA
scalers:
- type: azure-queue
  metadata:
    queueName: jobsqueue
    connectionFromEnv: STORAGE_CONNECTION

When moving from ACI to ACA:

# ARM template conversion example
# ACI original: 
"resources": [{
  "type": "Microsoft.ContainerInstance/containerGroups",
  "apiVersion": "2021-09-01"
}]

# ACA equivalent:
"resources": [{
  "type": "Microsoft.App/containerApps",
  "apiVersion": "2022-03-01"
}]

Key factors to evaluate:

• Stateful workloads require ACA volume mounts
• HTTP traffic benefits from ACA's ingress controller
• Short-lived tasks may still be cheaper in ACI

While both Azure Container Instances (ACI) and Azure Container Apps (ACA) provide serverless container solutions, they serve fundamentally different purposes in cloud architecture:

// ACI deployment example (single container)
az container create \
    --name myapp-container \
    --image myregistry.azurecr.io/myapp:v1 \
    --resource-group myResourceGroup \
    --ip-address Public

// ACA deployment example (scalable microservices)
az containerapp create \
    --name myapp-service \
    --resource-group myResourceGroup \
    --environment myContainerAppEnv \
    --image myregistry.azurecr.io/myapp:v1 \
    --target-port 80 \
    --ingress external \
    --min-replicas 1 \
    --max-replicas 10

ACA introduces Kubernetes-style scaling that ACI fundamentally lacks:

• Event-driven scaling: ACA supports scaling based on HTTP traffic, Kafka events, or custom metrics
• Replica management: ACA maintains application replicas while ACI provisions independent containers
• Dapr integration: Built-in service discovery and pub/sub patterns in ACA

The networking models differ significantly:

# ACI requires explicit networking configuration
az network vnet subnet create \
    --name aci-subnet \
    --vnet-name myVNet \
    --resource-group myResourceGroup \
    --address-prefixes 10.0.0.0/24

# ACA provides automatic service mesh capabilities
az containerapp ingress enable \
    --name myapp-service \
    --resource-group myResourceGroup \
    --type external \
    --target-port 80 \
    --transport auto

Cost structures reveal their different use cases:

Use ACI when:

• Running batch jobs or task-based workloads
• Need fast container startup for CI/CD pipelines
• Simple testing environments without scaling needs

Use ACA when:

• Building microservices architectures
• Requiring automatic scaling based on demand
• Implementing event-driven patterns
• Needing built-in service discovery