Container Logs¶

Testcontainers-Python provides several ways to access and follow container logs. This is essential for debugging and monitoring container behavior during tests.

Basic Log Access¶

The simplest way to access logs is using the get_logs method:

from testcontainers.generic import GenericContainer

with GenericContainer("nginx:alpine") as container:
    # Get all logs
    stdout, stderr = container.get_logs()
    print(f"STDOUT: {stdout}")
    print(f"STDERR: {stderr}")

Following Logs¶

To follow logs in real-time:

with GenericContainer("nginx:alpine") as container:
    # Follow logs
    for line in container.follow_logs():
        print(line)  # Each line as it appears

Log Access with Options¶

You can customize log access with various options:

with GenericContainer("nginx:alpine") as container:
    # Get logs with timestamps
    stdout, stderr = container.get_logs(timestamps=True)

    # Get logs since a specific time
    import datetime
    since = datetime.datetime.now() - datetime.timedelta(minutes=5)
    stdout, stderr = container.get_logs(since=since)

    # Get logs with tail
    stdout, stderr = container.get_logs(tail=100)  # Last 100 lines

Log Streams¶

You can access specific log streams:

with GenericContainer("nginx:alpine") as container:
    # Get only stdout
    stdout, _ = container.get_logs()

    # Get only stderr
    _, stderr = container.get_logs()

    # Get both streams
    stdout, stderr = container.get_logs()

Log Following with Callback¶

You can use a callback function to process logs:

def log_callback(line):
    print(f"Log line: {line}")

with GenericContainer("nginx:alpine") as container:
    # Follow logs with callback
    container.follow_logs(callback=log_callback)

Log Access in Tests¶

Here's how to use logs in tests:

import pytest
from testcontainers.generic import GenericContainer

def test_container_logs():
    with GenericContainer("nginx:alpine") as container:
        # Wait for specific log message
        for line in container.follow_logs():
            if "Configuration complete" in line:
                break

        # Verify log content
        stdout, stderr = container.get_logs()
        assert "Configuration complete" in stdout

Best Practices¶

Use appropriate log levels
Handle log streams separately
Use timestamps for debugging
Consider log rotation
Use log following for real-time monitoring
Clean up log resources
Use appropriate log formats
Consider log volume

Common Use Cases¶

Application Startup Verification¶

with GenericContainer("myapp:latest") as container:
    # Wait for application to start
    for line in container.follow_logs():
        if "Application started" in line:
            break

Error Detection¶

with GenericContainer("myapp:latest") as container:
    # Monitor for errors
    for line in container.follow_logs():
        if "ERROR" in line:
            print(f"Error detected: {line}")

Performance Monitoring¶

with GenericContainer("myapp:latest") as container:
    # Monitor performance metrics
    for line in container.follow_logs():
        if "Performance" in line:
            print(f"Performance metric: {line}")

Troubleshooting¶

If you encounter issues with log access:

Check container state
Verify log configuration
Check for log rotation
Verify log permissions
Check for log volume
Verify log format
Check for log buffering
Verify log drivers