Load balancing for single-address tenants

At a computer system that includes one or more processors and system memory, the computer system being configured as a load balancer that controls the routing of network packets between virtual addresses and destination addresses, a method for scaling up load balancing for a virtual address from a single destination address to a plurality of destination addresses, the method comprising:

• an act of the load balancer detecting that a virtual address that is being managed by the load balancer is to be scaled up from being associated with only a first destination address to being associated with at least an additional second destination address;
• in response to detecting, an act of the load balancer setting a flag for the virtual address to distinguish the virtual address from other virtual addresses that are associated with a single destination address;
• in response to detecting, an act of the load balancer sending a configuration message to a router, the configuration message interpretable by the router as an instruction to send network packets that are addressed to the virtual address to the load balancer, and cease a previous practice to bypass the load balancer for network packets that are addressed to the virtual address;
• and
• subsequent to sending the configuration message to the router, an act of the load balancer storing flow state for the virtual address.

A computer system, comprising:

• a router;
• a load balancer, the load balancer being configured to:
• detect that a virtual address of a tenant that is being managed by the load balancer is associated with only a single virtual machine instance of the tenant;
• in response to detecting, set a flag for the virtual address to distinguish the virtual address from other virtual addresses that are associated with multi-address tenants;
• in response to detecting, send a configuration message to the router, the configuration message interpretable by the router as an instruction to send network packets that are addressed to the virtual address to the virtual machine in a manner that bypasses the load balancer;
• refrain from storing subsequent flow state for the virtual address;
• detect that a virtual address that is being managed by the load balancer is to be scaled up from being associated with only a first destination address to being associated with at least an additional second destination address;
• in response to detecting, set a new flag for the virtual address to distinguish the virtual address from other virtual addresses that are associated with a single destination address;
• in response to detecting, send a new configuration message to the router, the new configuration message interpretable by the router as an instruction to send network packets that are addressed to the virtual address to the load balancer, and cease a previous practice to bypass the load balancer for network packets that are addressed to the virtual address;
• and
• subsequent to sending the new configuration message to the router, store flow state for the virtual address;
• and
• a virtualization host computer system that is configured to execute the virtual machine instance, the virtualization host computer system including a host agent that is configured to:
• detect that a network packet is addressed to the virtual address, and
• translate the network packet to be addressed to the virtual machine instance.