Load balancing

Load balancing configuration can be set for all Ambassador Edge Stack mappings in the ambassador Module, or set per Mapping. If nothing is set, simple round robin balancing is used via Kubernetes services.

To use advanced load balancing, you must first configure a resolver that supports advanced load balancing (e.g., the Kubernetes Endpoint Resolver or Consul Resolver). Once a resolver is configured, you can use the load_balancer attribute. The following fields are supported:

Supported load balancer policies:

• round_robin
• least_request
• ring_hash
• maglev

For more information on the different policies and the implications, see load balancing strategies in Kubernetes.

Round robin

When policy is set to round_robin, Ambassador Edge Stack discovers healthy endpoints for the given mapping, and load balances the incoming L7 requests with round robin scheduling. To specify this:

or, per mapping:

Note that load balancing may not appear to be "even" due to Envoy's threading model. For more details, see the Envoy documentation.

Least request

When policy is set to least_request, Ambassador Edge Stack discovers healthy endpoints for the given mapping, and load balances the incoming L7 requests to the endpoint with the fewest active requests. To specify this:

or, per mapping:

Sticky sessions / session affinity

Configuring sticky sessions makes Ambassador Edge Stack route requests to a specific pod providing your service in a given session. One pod serves all requests from a given session, eliminating the need for session data to be transferred between pods. Ambassador Edge Stack lets you configure session affinity based on the following parameters in an incoming request:

• Cookie
• Header
• Source IP

NOTE: Ambassador Edge Stack supports sticky sessions using two load balancing policies, ring_hash and maglev.

Cookie

If the cookie you wish to set affinity on is already present in incoming requests, then you only need the cookie.name field. However, if you want Ambassador Edge Stack to generate and set a cookie in response to the first request, then you need to specify a value for the cookie.ttl field which generates a cookie with the given expiration time.

Header

Ambassador Edge Stack allows header based session affinity if the given header is present on incoming requests.

Example:

Source IP

Ambassador Edge Stack allows session affinity based on the source IP of incoming requests.

Load balancing can be configured both globally, and overridden on a per mapping basis. The following example configures the default load balancing policy to be round robin, while using header-based session affinity for requests to the /backend/ endpoint of the quote application:

Load balancing can be configured both globally, and overridden on a per mapping basis.