Configuring Load Balancer Health Checks for PAS Routers
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This topic describes how to configure load balancer health checks for Pivotal Application Service (PAS) routers to ensure that the load balancer only forwards requests to healthy router instances. You can also configure a health check for your HAProxy if your deployment uses the HAProxy component.
In environments that require high availability, operators must configure their own redundant load balancer to forward traffic directly to the PAS routers. In environments that do not require high availability, operators can skip the load balancer and configure DNS to resolve the PAS domains directly to a single instance of a router.
Configure your load balancer to use the following HTTP health check endpoints. Add the IP addresses of all router instances along with their corresponding port and path.
- Gorouter (HTTP router):
- TCP router:
If you have deployed one or more instances of HAProxy between your infrastructure load balancer and Gorouters, configure your infrastructure load balancer to use the following HTTP health check endpoint:
The HAProxy is an optional component that provides some features that the Gorouter does not and can be helpful for demonstrating horizontal scalability of the PAS routers in environments where an infrastructure load balancer is not available.
To maintain high availability during upgrades to the Gorouter, each router is upgraded on a rolling basis. During upgrade of a highly available environment with multiple routers, each router is shut down, upgraded, and restarted before the next router is upgraded. This ensures that any pending HTTP request passed to the Gorouter are handled correctly.
PAS uses these properties:
Unhealthy threshold: Specifies the amount of time, in seconds, that the Gorouter continues to accept connections before shutting down. During this period, the health check reports
unhealthyto cause load balancers to fail over to other Gorouters. You should set this value greater than or equal to the maximum amount of time it could take your load balancer to consider a Gorouter instance unhealthy, given contiguous failed health checks.
Healthy threshold: Specifies the amount of time, in seconds, to wait until declaring the Gorouter instance started. This allows an external load balancer time to register the instance as
You can configure these properties in the Networking pane. For more information, see Configure Networking in Configuring PAS.
The image and table below describe the behavior of the load balancer health checks when a router shuts down and is restarted.
|1||A shutdown request is sent to the router.|
|2||The router receives shutdown request, which causes the following:
|3||The load balancer considers the router to be in an unhealthy state, which causes the load balancer to stop sending HTTP requests to the router.
The time between step 2 and 3 is defined by the values of the health check interval and threshold configured on the load balancer.
|4||The router shuts down.
The interval between step 2 and 4 is defined by the Unhealthy Threshold property of the Gorouter. In general, the value of this property should be longer than the value of the interval and threshold values (interval x threshold) of the load balancer. This additional interval ensures that any remaining HTTP requests are handled before the router shuts down.
|5||If the router shutdown is initiated by an upgrade, the Gorouter software is upgraded.|
|6||The router restarts. The router will return Service Unavailable responses for load balancer health checks for 20 seconds; during this time the routing table is preloaded.|
|7||The routers begins returning Service Available responses to the load balancer health check.|
|8||The load balancer considers the router to be in a healthy state. The time between step 7 and 8 is specified by the health check interval and threshold configured for your load balancer (health check threshold x health check interval).|
|9||Shutdown and upgrade of the other router begins.|