Stateless, affinity-preserving load balancing

A system comprising:

• a processing unit;
• and
• a routing component configured to facilitate load balancing among a plurality of hosts, wherein the routing component:
• receives a stream of packets;
• and
• interrogates a packet of the stream of packets for a session ID that uniquely identifies a packet session and for a tag indicating that the packet is a first packet of a packet session;
• and
• a routing function programmed to preserve session affinity in an event of a change in availability of one or more of the plurality of hosts, wherein the routing function at least partly responsive to the interrogation of the routing component:
• routes packets of the packet session to a host if the packet includes the tag;
• or
• routes the packet to an assigned host identified by the routing function if the packet does not include the tag;
• and
• the routing component further being configured to:
• generate a new routing function to provide a balanced distribution of sessions among the plurality of hosts based at least on change in availability of the plurality of hosts including for the packet session when the packet does not include the tag;
• and
• process the packet, including when the packet does not include the tag, in parallel based at least on both the new routing function and the routing function by applying a corresponding session ID to the new routing function and the routing function, such that the packet being processed is duplicated and sent to the hosts corresponding to the new routing function and the routing function.

One or more computer-readable storage devices having computer-executable instructions encoded thereon that, upon execution, configure the computer to perform operations comprising:

• receiving a stream of packets that forms a packet session;
• interrogating a packet of the stream of packets for a session ID and for a tag indicating that the packet is a first packet of the packet session;
• at least partly responsive to the interrogating:
• forwarding the packet to a host if the packet includes the tag;
• or
• delivering the packet to an assigned host identified by an existing routing function if the packet does not include the tag;
• responsive to a change in availability of one or more hosts of a plurality of hosts, generating a new routing function to provide a substantially balanced distribution of sessions among the plurality of hosts including for the packet session when the packet does not include the tag;
• and
• processing the packet, including when the packet does not include the tag, in parallel based at least on both the new routing function and the existing routing function by applying a corresponding session ID to the new routing function and the existing routing function, such that the packet being processed is duplicated and sent to the hosts corresponding to the new routing function and the existing routing function.