Introduction
Operating system supportSafeKit Farm architecture
Network load balancing and failover
The farm architecture provides both network load balancing, through transparent distribution of network traffic, and software and hardware failover.
This architecture provides a simple solution to increasing system load. The same application runs on each server, and the load is distributed across the network stacks of the servers by an extension of the OS.
Farm architecture is suited to front-end applications like firewalls and web services.
Netfilter.Safe, Apache_farm.Safe, and Microsoft IIS_farm.safe are examples of farm application modules. You can write your own farm module for your application, based on the generic module Farm.safe.
Virtual IP addresses with network load balancing
All the N servers in a cluster are associated with a single virtual IP address. The input traffic for this address is received by all the N servers and split among them by a filter inside each server's kernel. Once accepted by one server, only the CPU and memory of this server are used by the application responding to the client's requests: the output messages are then sent directly from the application server to the client. If a server fails, the SafeKit membership protocol reconfigures the filters in the farm to re-balance the traffic on the remaining available servers.
Setting each server to take more or less network load
Each server can be configured with a weight, to take more or less traffic: the distribution of traffic to each server is calculated in proportion to its weight value.
Load balancing on client IP address for stateful servers
You can configure the load-balancing algorithm to operate on the identity of client packets. With load balancing configured on the client IP address, the same client is always connected to the same server through successive TCP sessions: this preserves the client context.
Other algorithms are proposed for stateless applications, UDP services, firewalls,... In particular, with load balancing on client TCP session ID rather than on client IP address, the same client will have TCP sessions successively distributed across the different servers in the farm.
The ideal solution for farm architectures with 2 to 10 servers
In terms of price and functionality, SafeKit's software load balancing is optimal for small and medium-sized server farms, typically with 2 to 10 servers. For larger farms, investing in costlier load-balancing network boxes becomes a viable option.
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