Chapter 5. Skupper load balancing and failover

Skupper enables load balancing and failover across servers located across the application network. Specifically, Skupper balances active TCP connections across workloads deployed in distinct sites. If a workload at one site becomes unavailable, traffic is automatically rerouted to available sites. For example, if you deploy the same backend code on two sites and expose the backend on the application network, concurrent requests from a third site to the backend service are processed by both sites.

In an application network, the routing algorithm attempts to use the path with the lowest total cost from client to target server.

Understanding link cost

Link cost is a configurable value when creating links between sites. In the earlier example, the link cost from the client to each server is the same by default (1). However, if one server is more powerful and has better latency, it processes TCP requests more quickly, resulting in more traffic being directed to that server. Skupper determines the perceived cost with the context of knowing the configured cost and the current number of open TCP connections and directs traffic to the server with the lowest cost.

📌 NOTE Traffic load is based on the number of concurrent TCP connections, so 'round robin' behavior should not be expected.

Using Skupper load balancing to achieve failover

You can configure the network so that a specific location handles all traffic until failure. After failure at that location, all traffic is handled by a different location. To achieve this behavior, you set the cost from the client to the backup server high, for example 9999, as described in {cost-link}.

📌 NOTE Link cost is configured for all services between two sites. It is currently not possible to set different costs for distinct services.