Load balancing of Jobtechs openshift clusters
Improving availability of Jobtech services with load balancing over multiple openshift clusters
In order to further improve the availability of Jobtech services we are exploring load balancing over multiple Openshift clusters.
An Openshift cluster in itself is highly available, and with the deployment we use we can loose an entire worker node and the workloads will evacuate to other worker nodes in order to regain redundancy. In normal cases this means no service interuptions will be noticeable, since workloads are usually deployed redundantly.
However, if the entire cluster fails, we are out of luck. This is not a hypothetical scenario, it happened once because of certificate expirations that went unnoticed.
Deploying new Openshift clusters at other cloud providers is quite feasible since Openshift 4.2 where the installer was much improved since the previous versions we have been using, 3.10 and 3.11.
Deploying our services reduntantly over several clusters is also something we have explored using the skopeo command to copy images between clusters.
The remaining problem, then, is how to load balance between several different clusters.
Several options where evaluated:
DNS round robin. This is simple, but not reliable. DNS record TTL makes it difficult to fail-over between clusters reliably
Client based routing. This will increase complexity at the client side. This is reliable and gives the client and opportunity to decide what to do during backend outtages.
External load balancer service that spans over cloud providers.
We believe using an external load balancer service such as Cloudflare will make it easy to implement our API:s, and it can co-exist with client based routing for organizations that need greater control.
We will explore Cloudflare next.
First we need a hello-world service in each cluster we are going to be load balancing between.
test.services.jtech.se and jave.services.jtech.se clusters will be used. The endpoint will be called hello.platsbanka.nu
Platsbanka.nu is a debug domain at Loopia that was used for this test. We also made a lbjobtechdev.se domain at AWS route53, but there were problems propagating the DNS SOA and NS record changes needed to use Cloudflare, so we couldn’t use this domain for these tests.
In each cluster do:
oc new-project hello oc new-app openshift/hello-openshift oc expose svc/hello-openshift
Then set the environment variable RESPONSE in the deployment to something that identifies the cluster and create the route.
oc expose svc/hello-openshift --hostname=hello.platsbanka.nu --name=hello-openshift-cloudflare-pool oc set env dc/hello-openshift RESPONSE="this is the JAVE/TEST cluster"
Create a load balancer service in Cloudflare, and create a pool, hello-pool. Origin servers will be hello.jave.services.jtech.se and hello.test.services.jtech.se. These DNS names will resolve to the respective clusters. Each cluster must then route hello.platsbanka.nu to the correct service when a corresponding http request arrives from Cloudflare.
If you reload “hello.platsbanka.nu” repeatedly, Cloudflare will round robin between the two clusters, the message will vary depending on which cluster answers. Cloudflare will decide which cluster to route to according to its own algorithm, and the weight assigned to each cluster in the load balancer.
If you are too lazy to press reload in a browser you can of course use curl.
while true; do curl hello.platsbanka.nu;done this is the JAVE cluster this is the test cluster this is the test cluster this is the test cluster this is the JAVE cluster this is the test cluster
When you get tired of this, press ctrl-c.