ssh-tunnel-swarm

Bash tool for running a swarm of SSH tunnels — forward and reverse, many hosts at once — off one rules file. No daemon, no config DSL beyond plain text, just ssh -L/ssh -R looped forever per host with auto-reconnect.

Security & safety

• This opens real SSH connections using your keys to hosts you list in the rules file — anything wrong in that file connects somewhere real.
• Reverse tunnels (reverse) expose a LOCAL service to the REMOTE host. Only point reverse rules at hosts you trust — a compromised or malicious remote can now reach whatever you bound on your side.
• Forward tunnels (forward) expose a REMOTE service through YOUR local machine. Same trust logic in reverse: don't forward into networks you don't control.
• All connections force StrictHostKeyChecking=yes — the target host must already be in known_hosts or the connection fails. That's intentional; don't work around it by disabling host key checking.
• No password auth support — private key only. Keep the key file permissions tight (chmod 600) and never put keys or the rules file (which references key paths) in a world-readable location or a git repo.
• Every connection block runs forever in a retry loop (5s backoff) until you kill it — make sure that's actually what you want before pointing this at a host.

When to use

• Standing up several forward and/or reverse SSH tunnels across one or many hosts from a single declarative file, instead of hand-rolling a pile of ssh -L/ssh -R commands or systemd units.
• Tunnels need to survive disconnects — the tool loops and reconnects automatically.
• Exposing a local dev service to a remote box (reverse), or reaching a remote-network-only service from your machine (forward).

When NOT to use

• One-off, single tunnel for a few minutes — just run ssh -L/ssh -R directly.
• Password-based SSH auth — this tool only supports private key auth.
• You need a full VPN / mesh network (e.g. overlay networking, NAT traversal across many peers) — this is tunnels over plain SSH, not a VPN.

Config grammar (rules file)

Plain text file, default path rules.txt, overridable via RULES_FILE. It's a sequence of connection blocks, separated by blank lines. Each block:

<line 1>  user@host:port=/path/to/private/ssh/key
<line 2+> forward|reverse local-interface:local-port:remote-interface:remote-port
          ... (one or more tunnel lines)

• Header line — exactly one per block, always first: user@hostname:port=/path/to/private/key
  • user — [a-zA-Z0-9._-]+
  • hostname — hostname or IPv4 (no scheme, no special chars)
  • port — SSH port on the remote host, 0-65535
  • =/path/to/key — path to the private key for THIS connection; must exist on disk or the tool refuses to start (FATAL at load time).
• Tunnel lines — one or more per block, every line until the next blank line or EOF: direction local-interface:local-port:remote-interface:remote-port
  • direction is literally forward or reverse, nothing else.
  • all four of interface/port/interface/port are required, colon-separated, no spaces.
  • reverse → ssh -R remote-interface:remote-port:local-interface:local-port (binds on the REMOTE host, forwards back to your LOCAL interface:port).
  • forward → ssh -L local-interface:local-port:remote-interface:remote-port (binds on your LOCAL interface, forwards to something reachable FROM the remote host).
• Blank line = end of the current block / start of the next. Multiple blocks = multiple independent SSH connections, each supervised in its own background loop.
• One host can carry any number of forward and reverse tunnel lines mixed together.

Example ruleset (forward + reverse, two hosts)

# Host 1: expose a local web app on the VPS (reverse), and reach the VPS's
# internal Postgres from your machine (forward).
deploy@vps1.example.com:22=/home/user/.ssh/deploy_vps1
reverse 0.0.0.0:8080:localhost:3000
forward localhost:15432:127.0.0.1:5432

# Host 2: reach an internal-only admin panel through a jump host (forward),
# and expose your local dev API back to that jump host (reverse).
opsuser@jump.example.com:22=/home/user/.ssh/deploy_jump
forward localhost:9090:10.0.5.20:9090
reverse 127.0.0.1:4000:localhost:4000

With the above: curl http://vps1.example.com:8080 hits your local localhost:3000; psql -h localhost -p 15432 reaches the VPS's internal Postgres; curl http://localhost:9090 on your machine reaches 10.0.5.20:9090 through the jump host; and the jump host's localhost:4000 reaches your local dev API on 4000.

Running it

No subcommands, no CLI flags — everything is env vars, one invocation runs the swarm in the foreground until killed:

RULES_FILE=/path/to/rules.txt \
LOG_ENABLED=1 \
LOG_FILE=/path/to/log/file \
LOG_LEVEL=DEBUG \
ssh-tunnel-swarm

Ctrl-C (SIGINT) or SIGTERM kills every tunnel connection cleanly and exits.

Install/build details, the full env var reference, and log-level semantics are in references/setup.md.