Azure Webapp Ssh Operations

Downloading Files via stdout

# Download by redirecting remote file to stdout
download_command = f"cat {remote_file}"

result = subprocess.run(
    ['az', 'webapp', 'ssh', '--name', app_name, '--resource-group', rg],
    input=download_command + '\nexit\n',
    capture_output=True,  # Binary stdout
    timeout=120
)

# Write binary stdout to local file
with open(local_file, 'wb') as f:
    f.write(result.stdout)

Verification Pattern

def verify_app_service(app_name: str, resource_group: str) -> bool:
    """Check if App Service is accessible before SSH operations."""
    result = subprocess.run(
        ['az', 'webapp', 'show', '--name', app_name, '--resource-group', resource_group],
        capture_output=True,
        text=True,
        check=False
    )
    return result.returncode == 0

Prerequisites

• Azure CLI installed (az --version)
• Authenticated session (az login, check with az account show)
• Target is Linux App Service (Windows doesn't support SSH)
• SSH access enabled (default for Linux containers)

Limitations

• Timeout risk: Large files or slow operations need appropriate timeout values (120s+ recommended)
• Binary data: Use capture_output=True without text=True for binary downloads
• Session cleanup: Always send exit\n after commands to prevent hanging sessions
• Error detection: Check for success markers (e.g., echo SUCCESS) since exit codes may not propagate reliably through SSH

Common Use Cases

Backup /home/data directory

# 1. Create remote tar
tar_cmd = "tar -czf /tmp/data.tar.gz -C /home data && echo SUCCESS"
result = subprocess.run(
    ['az', 'webapp', 'ssh', '--name', app, '--resource-group', rg],
    input=tar_cmd + '\nexit\n',
    capture_output=True,
    text=True,
    timeout=120
)

# 2. Download tar
download_cmd = "cat /tmp/data.tar.gz"
result = subprocess.run(
    ['az', 'webapp', 'ssh', '--name', app, '--resource-group', rg],
    input=download_cmd + '\nexit\n',
    capture_output=True,
    timeout=120
)
with open('backup.tar.gz', 'wb') as f:
    f.write(result.stdout)

Restore data directory

# Upload via stdin redirection not directly supported
# Alternative: Use az webapp deployment source config-zip or Kudu API

Anti-Patterns

• Using text=True for binary data — corrupts downloads
• No timeout — hangs indefinitely on stuck commands
• Forgetting exit command — leaves SSH sessions open
• Assuming exit codes work — check stdout markers instead

Why Not Alternatives?

SSH provides direct filesystem access with only Azure CLI dependency.