Stream container logs

What this covers

The log stream shows container output in real time. Use it to debug startup problems, watch live traffic and observe how the app behaves during testing. Streaming is for live visibility. If you also need persisted history, turn on container logging (filesystem or Log Analytics). This page covers streaming for both App Service and Azure Container Apps, because the commands and gotchas differ.

Exam weight: Develop containerized solutions on Azure (20–25%)

Skills measured

• "Monitor and troubleshoot solutions on AKS and Container Apps by inspecting logs, events, and end-to-end connectivity"
• "Deploy containers to Azure App Service, including configuring App Service to supply environment variables and secrets"

Key concepts

App Service log stream

• CLI command: az webapp log tail.
• Portal path: Web App, then Monitoring > Log stream.
• The browser and the terminal show the same real-time output.
• Press Ctrl+C to stop streaming in the CLI.
• Scaled-out apps: the stream shows output from all instances, and each line includes an instance identifier.
• For Linux containers, stdout/stderr only reach the stream after you turn on container logging: az webapp log config --docker-container-logging filesystem.

Container Apps log stream

• CLI command: az containerapp logs show --follow. --type console (the default) shows your app's output. --type system shows platform events.
• --tail returns the last n lines (0–300, default 20).
• With several revisions, replicas or containers, narrow it with --revision, --replica and --container.
• az containerapp env logs show --follow streams environment-wide system logs.
• If a revision is scaled to zero, there's nothing to stream. Set min replicas to 1 while debugging.

Best for

Startup failures, live debugging and short test sessions. Don't rely on it alone for long-term retention.

How it works

The stream is a live tail of the same pipeline that writes persisted logs. When you disconnect, nothing is kept unless a persistent destination is configured.

Hands-on

Azure portal

1. Open the web app (or container app) in the Azure portal.
2. Under Monitoring, select Log stream.
3. Watch the same real-time container output in the browser viewer. In Container Apps, switch between Console and System, and pick a revision, replica and container.

Azure CLI

App Service:

az webapp log config \
  --resource-group myResourceGroup \
  --name myDocumentProcessor \
  --docker-container-logging filesystem

az webapp log tail \
  --resource-group myResourceGroup \
  --name myDocumentProcessor

The log stream shows new entries as they appear. Stop it with Ctrl+C. If console lines don't show up straight away, wait about 30 seconds.

Container Apps:

az containerapp logs show -n quote-api -g quote-api-rg --type console --follow
az containerapp logs show -n quote-api -g quote-api-rg --type system --tail 50

az containerapp replica list -n quote-api -g quote-api-rg --revision <revision-name> \
  --query "[].{name:name, containers:properties.containers[].name}"
az containerapp logs show -n quote-api -g quote-api-rg \
  --revision <revision-name> --replica <replica-name> --container quote-api --follow

Python

Write logs to stdout so the stream (and Log Analytics) can pick them up:

import logging
import sys

logging.basicConfig(stream=sys.stdout, level=logging.INFO,
                    format="%(asctime)s %(levelname)s %(message)s")
logging.info("quote-api started")

Exam traps

Quick review

• App Service: az webapp log tail. Portal: Monitoring > Log stream.
• Turn on --docker-container-logging filesystem so stdout reaches the stream.
• Scaled-out apps stream all instances, and each line carries an instance id.
• Container Apps: az containerapp logs show --follow --type console|system.
• --tail defaults to 20 lines, with a maximum of 300.
• Use cases: a container that won't start, validating a fix live, traffic spikes, port or bind mistakes.

Practice

• Practice: Container troubleshooting questions
• Practice: App Service container questions

Official references

• Stream logs in App Service
• az webapp log
• View log streams in Azure Container Apps
• Related topics: Configure container logs and Diagnostic console (Kudu)
• AI-200 study guide