Scaling Mosh with an External Load Balancer

Packets drop. Connections freeze. Latency spikes hit like a hammer. You know the pain when remote access breaks mid-command. Mosh fixes that—its adjustable protocol keeps sessions alive over unstable networks. But scaling Mosh beyond a single server used to be a dead end. The answer is a Mosh External Load Balancer.

A Mosh External Load Balancer routes incoming Mosh sessions across multiple servers while preserving state. Unlike TCP-based SSH, Mosh runs over UDP. That changes the rules for load distribution. Traditional load balancers fail here because UDP is stateless from their perspective. Mosh keeps a persistent key exchange between client and server—if the stream breaks, the session dies. The solution is a load balancer designed for Mosh’s UDP handshake.

Setting up a Mosh External Load Balancer starts with selecting a UDP-aware system: HAProxy with UDP mode, NGINX stream module, or dedicated tools like LVS. You configure it to forward UDP packets on the default Mosh port range (usually 6000–6100). Health checks ensure only active backend servers receive traffic. Session affinity is critical; without it, user connections will bounce to a backend that doesn’t know them. IP hash or consistent hashing solves this.

After packet routing, the network layer must be tuned for low latency. This means enabling fast failover, keeping ephemeral ports open in firewalls, and tuning kernel parameters like net.ipv4.udp_rmem_min for buffer management. Monitor with mosh-server --verbose logs and packet traces to confirm traffic paths.

A Mosh External Load Balancer unlocks horizontal scalability for remote access over weak connections. Developers on the edge of networks—ships, rural sites, satellite links—can connect to the closest node in a global cluster without losing state. UDP-based load balancing is not a luxury feature; it’s a prerequisite for high availability in Mosh deployments.

Stop treating Mosh as a single-host tool. Deploy a Mosh External Load Balancer and scale it like any critical service. See it live in minutes at hoop.dev.