Load Balancer Mosh

The SSH window flickers, the connection dies, and your deploy grinds to a halt. You reload. You reconnect. You swear. Then you remember Mosh.

Load Balancer Mosh is the missing link between modern infrastructure scaling and reliable terminal access. Mosh—short for mobile shell—keeps sessions alive across network drops, IP changes, and roaming between networks. It’s built for unstable connections. But when you place Mosh behind a load balancer, you face one strict problem: it’s not plain TCP like SSH. Mosh uses UDP. Traditional load balancers default to TCP health checks, routing, and sticky sessions. With Mosh, that won’t cut it.

To run Mosh reliably in a scaled environment, you need load balancer rules that pass UDP traffic with persistence. UDP session persistence means the client stays pinned to one backend node until the connection ends. Without it, packets will hit different servers, and the session will break. On AWS, this means configuring a Network Load Balancer with UDP listeners. On bare metal or self-hosted setups, it means tools like HAProxy or NGINX configured for UDP proxy mode.

One core Mosh detail: it starts with SSH for authentication, then switches to high-numbered UDP ports for the session. Your load balancer must forward those UDP ports exactly, no NAT rewriting mid-stream, no rebalancing. Security is critical—weigh firewall rules, ephemeral port ranges, and ensure only expected ports open between client and Mosh server. Many engineers forget to align firewall settings to match load balancer forwarding rules, leading to silent failures that feel like packet loss.

When scaling Mosh deployments across multiple instances, automation matters. Use orchestration to update backend pools dynamically as nodes join or leave. Log UDP traffic patterns to track user sessions. Monitor with metrics from packet-level counters, not TCP-based assumptions. The operational mindset must shift from connection-oriented load balancing toward packet-forwarding accuracy.

If your engineering culture emphasizes uptime, latency, and fault tolerance, building UDP-friendly load balancers for Mosh is not optional—it’s table stakes. Done right, it allows remote admins, developers, and ops teams to maintain shell sessions through deploys, failovers, and global network chaos.

Run it, test it, break it, fix it fast. See Load Balancer Mosh in action today—spin it up in minutes with hoop.dev.