terraform.md

Building Kubernetes clusters with Terraform

Kops can generate Terraform configurations, and then you can apply them using the terraform plan and terraform apply tools. This is very handy if you are already using Terraform, or if you want to check in the Terraform output into version control.

The gist of it is that, instead of letting kops apply the changes, you tell kops what you want, and then kops spits out what it wants done into a .tf file. You are then responsible for turning those plans into reality.

The Terraform output should be reasonably stable (i.e. the text files should only change where something has actually changed - items should appear in the same order etc). This is extremely useful when using version control as you can diff your changes easily.

Note that if you modify the Terraform files that kops spits out, it will override your changes with the configuration state defined by it's own configs. In other terms, kops own state is the ultimate source of truth (as far as kops is concerned), and Terraform is a representation of that state for your convenience.

Ps: Steps below assume a recent version of Terraform. There's a workaround for a bug if you are using a Terraform version before 0.7 that you should be aware of (see "Caveats" section).

Using Terraform

Set up remote state

You could keep your Terraform state locally, but we strongly recommend saving it on S3 with versioning turned on on that bucket. Configure a remote S3 store like so:

$ terraform remote config \
  -backend=s3 \
  -backend-config="bucket=mycompany.terraform>" \
  -backend-config="key=infrastructure.tfstate" \
  -backend-config="region=us-east-1"

Learn more about Terraform state here.

Initialize/create a cluster

For example, a complete setup might be:

$ kops create cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes \
  --dns-zone=kubernetes.mydomain.com \
  [... your other options ...]
  --out=. \
  --target=terraform

The above command will create kops state on S3 (defined in --state) and output a representation of your configuration into Terraform files. Thereafter you can preview your changes and then apply as shown below:

$ terraform plan
$ terraform apply

Wait for the cluster to initialize. If all goes well, you should have a working Kubernetes cluster!

Editing the cluster

It's possible to use Terraform to make changes to your infrastructure as defined by kops. In the example below we'd like to change some cluster configs:

$ kops edit cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes

# editor opens, make your changes ...

Then output your changes/edits to kops cluster state into the Terraform files. Run kops update with --target and --out parameters:

$ kops update cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes \
  --out=. \
  --target=terraform

Then apply your changes after previewing what changes will be applied:

$ terraform plan
$ terraform apply

Ps: You aren't limited to cluster edits i.e. kops edit cluster. You can also edit instances groups e.g. kops edit instancegroup nodes|bastions etc.

Teardown the cluster

When you eventually terraform destroy the cluster, you should still run kops delete cluster, to remove the kops cluster specification and any dynamically created Kubernetes resources (ELBs or volumes). To do this, run:

$ terraform plan -destroy
$ terraform destroy
$ kops delete cluster --yes \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes

Ps: You don't have to kops delete cluster if you just want to recreate from scratch. Deleting kops cluster state means that you've have to kops create again.

Caveats

Workaround for Terraform <0.7

Before terraform version 0.7, there was a bug where it could not create AWS tags containing a dot. We recommend upgrading to version 0.7 or laster, which will fix this bug. Please note that this issue only affects the volumes.

There's a workaround if you need to use an earlier version. We divide the cloudup model into three parts:

• models/config which contains all the options - this is run automatically by "create cluster"
• models/proto which sets up the volumes and other data which would be hard to recover (e.g. likely keys & secrets in the near future)
• models/cloudup which is the main cloud model for configuring everything else

The workaround is that you don't use terraform for the proto phase (you can't anyway, because of the bug!):

$ kops create cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes \
  [... your other options ...]
  --out=. \
  --target=terraform

$ kops update cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes \
  --model=proto \
  --yes

And then you can use terraform to do the remainder of the installation:

$ kops update cluster \
  --name=kubernetes.mydomain.com \
  --state=s3://mycompany.kubernetes \
  --model=cloudup \
  --out=. \
  --target=terraform

Then, to apply using terraform:

$ terraform plan
$ terraform apply

You should still run kops delete cluster ${CLUSTER_NAME}, to remove the kops cluster specification and any dynamically created Kubernetes resources (ELBs or volumes), but under this workaround also to remove the primary ELB volumes from the proto phase.