Implementing a Composition with functions Demo

We want to define a new resource AcmeDatabase(XRC), XAcmeDatabase(XR), to create CloudSQL PG instances (DatabaseInstance).

We have two environments, dev and prod, for both of them we have some environment-specific configurations.

We want to let users specify wether they want to have a Database created too, but if specified, the Database can only be created once the DatabaseInstance is ready.

Developing it

We define the Provider we need.
We define our XRD.
We define our environment specific configurations as EnvironmentConfigs.
We define our Composition and all the functions required.

Composition logic

In pseudocode the above Composition logic could look like this:

# function-environment-configs
environment := getEnvironmentConfig(xr.spec.environment)

# function-patch-and-transform
desiredState := getDesiredResources(xr, environment)

# function-sequencer
desiredState = filterDatabaseIfDatabaseInstanceNotReady(desiredState)

# function-cel-filter
desiredState = filterDatabaseIfNotNeeded(xr, desiredState)

return desiredState

Checking it locally

We can write a few examples:

xr-dev.yaml: a DatabaseInstance with the dev environment configuration.
xr-dev-with-db.yaml: a DatabaseInstance and a Database with the dev environment configuration.
xr-prod.yaml: a Database with the prod environment configuration.
xr-prod-bigger.yaml: a Database with a larger disk than the default, 100GB.

We can then render them all locally to see everything works as expected:

crossplane beta render examples/xr-dev.yaml setup/composition.yaml setup/functions.yaml --extra-resources=setup/environmentConfigs.yam

crossplane beta render examples/xr-dev-with-db.yaml setup/composition.yaml setup/functions.yaml --extra-resources=setup/environmentConfigs.yam

crossplane beta render examples/xr-prod.yaml setup/composition.yaml setup/functions.yaml --extra-resources=setup/environmentConfigs.yam

crossplane beta render examples/xr-prod-bigger.yaml setup/composition.yaml setup/functions.yaml --extra-resources=setup/environmentConfigs.yam

Have a look at crossplane beta validate to validate the rendered resources against their schema.

Running it

Create a new control plane

kind create cluster
helm install crossplane crossplane-stable/crossplane --namespace crossplane-system --create-namespace

Setup

We'll first need to create a Secret with the GCP credentials, see the docs for more details on how to get the token in the first place.

kubectl create secret generic gcp-secret -n crossplane-system --from-file=creds=../gcp-credentials.json

Now we can apply all the requirements:

kubectl apply -f setup

Apply

Once all the requirements are successfully installed we can apply one of our examples and check it works as intended.

kubectl apply -f examples/xr-dev-with-db.yaml

crossplane beta trace xacmedatabases.acme.com acme-db-dev -o wide

phisco / xp-demo-level-up