GCP provides several types of load balancer as follows:
- Layer 4 TCP LoadBalancer
- Layer 4 UDP LoadBalancer
- Layer 7 HTTP(S) LoadBalancer
The Layer 4 LoadBalancers (both TCP and UDP) are similar to AWS Classic ELB. On the other hand, the Layer 7 HTTP(S) LoadBalancer has content (context)-based routing. For example, the URL/image will forward to instance-a; everything else will forward to instance-b. So, it's more like an application-level LoadBalancer.
In order to set up LoadBalancer, and unlike AWS ELB, there are several steps you'll need to follow in order to configure some items beforehand:
|
Configuration item |
Purpose |
|
Instance group |
Determine a group of VM instances or a VM template (OS image). |
|
Health check |
Set health threshold (interval, timeout, and so on) to determine instance group health status. |
|
Backend service |
Set load threshold (maximum CPU or requests per second) and session affinity (sticky session) to the instance group and associate it to health check. |
|
url-maps (LoadBalancer) |
This is an actual place-holder to represent an L7 LoadBalancer that associates backend services and targets the HTTP(S) proxy. |
|
Target HTTP(S) proxy |
This is a connector that makes relationships between frontend forwarding rules to LoadBalancer. |
|
Frontend forwarding rule |
Associate between the Target HTTP proxy and IP address (ephemeral or static) and port number. |
|
External IP (static) |
(Optional) allocate a static external IP address for LoadBalancer. |
The following diagram is for all of the preceding components' association that constructs the L7 LoadBalancer:
Let's set up an instance group first. In this example, there are three instance groups to create: one for the private hosted Tomcat instance (8080/tcp) and another two instance groups for public HTTP instances for each zone.
To do that, execute the following commands to group three of them:
//create instance groups for HTTP instances and tomcat instance
$ gcloud compute instance-groups unmanaged create http-ig-us-west --zone us-west1-a
$ gcloud compute instance-groups unmanaged create http-ig-us-east --zone us-east1-c
$ gcloud compute instance-groups unmanaged create tomcat-ig-us-west --zone us-west1-a
//because tomcat uses 8080/tcp, create a new named port as tomcat:8080
$ gcloud compute instance-groups unmanaged set-named-ports tomcat-ig-us-west --zone us-west1-a --named-ports tomcat:8080
//register an existing VM instance to correspond instance group
$ gcloud compute instance-groups unmanaged add-instances http-ig-us-west --instances public-on-subnet-a --zone us-west1-a
$ gcloud compute instance-groups unmanaged add-instances http-ig-us-east --instances public-on-subnet-b --zone us-east1-c
$ gcloud compute instance-groups unmanaged add-instances tomcat-ig-us-west --instances private-on-subnet-a --zone us-west1-a