Scribbles for my memory

autossh has its own connection monitoring that opens an extra port for heartbeats. But this is redundant — SSH already has native keepalive via ServerAliveInterval. The extra port can even cause problems if it's not available on the remote side.

The modern approach: disable autossh's built-in monitoring with -M 0 and let SSH's native heartbeats handle it. When SSH detects a dead connection (after ServerAliveInterval * ServerAliveCountMax seconds of no response), autossh automatically reconnects.

Put everything in ~/.ssh/config:

Host gateway
    HostName your-gateway-ip
    User ec2-user
    ServerAliveInterval 30
    ServerAliveCountMax 3
    LocalForward 8080 internal-soap-ec2:8080

Then the command reduces to:

autossh -M 0 -Nf gateway

-M 0 is the only autossh-specific flag you need. Everything else — host, user, keepalive, even the tunnel — lives in SSH config where it belongs. ServerAliveInterval 30 sends a heartbeat every 30 seconds through the SSH port itself (no extra ports needed), and ServerAliveCountMax 3 means 90 seconds of silence triggers a disconnect detection.