Add documentation for MRDs, MRAPs, and safe-start

content/master/guides/disabling-unused-managed-resources.md

@@ -0,0 +1,214 @@
+---
+title: Disabling Unused Managed Resources
+weight: 85
+state: alpha
+alphaVersion: 2.0
+description: Reduce CRD overhead by disabling unused managed resources
+---
+
+{{<hint "important">}}
+This guide uses
+[managed resource definitions]({{<ref "../managed-resources/managed-resource-definitions">}})
+and
+[managed resource activation policies]({{<ref "../managed-resources/managed-resource-activation-policies">}}),
+which Crossplane v2.0+ enables by default. To disable this behavior, set
+`--enable-custom-to-managed-resource-conversion=false` when installing
+Crossplane.
+{{</hint>}}
+
+Large Crossplane providers can install 100+ managed resource CRDs, consuming
+significant cluster resources even when you only need one or two resource
+types. This guide shows how to use
+[ManagedResourceDefinitions]({{<ref "../managed-resources/managed-resource-definitions">}})
+and
+[ManagedResourceActivationPolicies]({{<ref "../managed-resources/managed-resource-activation-policies">}})
+to install only the provider resources you actually need.
+
+## Before you begin
+
+This guide requires:
+
+- Crossplane v2.0+ installed in your cluster
+- A provider with `safe-start` capability (this guide uses
+  `provider-aws-ec2:v2.0.0`)
+- Basic familiarity with Kubernetes and Crossplane concepts
+
+{{<hint "important">}}
+ManagedResourceDefinitions and ManagedResourceActivationPolicies are alpha
+features in Crossplane v2.0+.
+{{</hint>}}
+
+## The problem: Resource overhead
+
+Installing a large cloud provider in Crossplane creates hundreds of CRDs:
+
+```shell
+# Before selective activation - provider-aws-ec2 installs ~200 CRDs
+kubectl get crds | grep aws.crossplane.io | wc -l
+# Output: 200
+
+# Each CRD consumes ~3 MiB of API server memory
+# 200 CRDs × 3 MiB = 600 MiB of memory usage
+```
+
+Most users only need a small subset of these resources. Selective activation
+lets you install just what you need.
+
+## Step 1: Disable automatic activation
+
+By default, the Crossplane Helm chart creates an activation policy that
+enables all provider resources. To use selective activation, disable this
+default behavior.
+
+<!-- vale Google.Headings = NO -->
+### Option A: Helm installation
+<!-- vale Google.Headings = YES -->
+
+```shell
+helm install crossplane crossplane-stable/crossplane \
+  --namespace crossplane-system \
+  --create-namespace \
+  --set provider.defaultActivations={}
+```
+
+<!-- vale Google.Headings = NO -->
+### Option B: Existing installation
+<!-- vale Google.Headings = YES -->
+
+Delete the default activation policy:
+
+```shell
+kubectl delete managedresourceactivationpolicy default
+```
+
+## Step 2: Install your provider
+
+Install your provider as normal. Crossplane automatically converts the
+provider's CRDs to ManagedResourceDefinitions:
+
+```yaml
+apiVersion: pkg.crossplane.io/v1
+kind: Provider
+metadata:
+  name: provider-aws-ec2
+spec:
+  package: xpkg.crossplane.io/provider-aws-ec2:v2.0.0
+```
+
+Save this as `provider.yaml` and apply it:
+
+```shell
+kubectl apply -f provider.yaml
+
+# Wait for provider to be ready
+kubectl wait --for=condition=Healthy provider/provider-aws-ec2 --timeout=5m
+```
+
+## Step 3: Verify Crossplane created MRDs
+
+<!-- vale Google.WordList = NO -->
+After the provider installs, check ManagedResourceDefinitions that Crossplane
+created in inactive state:
+<!-- vale Google.WordList = YES -->
+
+```shell
+# List ManagedResourceDefinitions
+kubectl get managedresourcedefinitions
+
+# Check their states (should be "Inactive")
+kubectl get mrds -o jsonpath='{.items[*].spec.state}' \
+  | tr ' ' '\n' | sort | uniq -c
+# 200 Inactive
+```
+
+Notice that Crossplane didn't create any CRDs yet:
+
+```shell
+kubectl get crds | grep ec2.aws.m.crossplane.io
+# No output - CRDs don't exist until MRDs are activated
+```
+
+## Step 4: Create an activation policy
+
+Create a ManagedResourceActivationPolicy to selectively activate only the
+resources you need:
+
+```yaml
+apiVersion: apiextensions.crossplane.io/v1alpha1
+kind: ManagedResourceActivationPolicy
+metadata:
+  name: my-app-resources
+spec:
+  activate:
+  - instances.ec2.aws.m.crossplane.io        # EC2 instances for compute
+  - securitygroups.ec2.aws.m.crossplane.io   # Security groups for networking
+  - vpcs.ec2.aws.m.crossplane.io             # VPCs for isolation
+```
+
+Save this as `activation-policy.yaml` and apply it:
+
+```shell
+kubectl apply -f activation-policy.yaml
+```
+
+## Step 5: Verify selective activation
+
+<!-- vale Google.WordList = NO -->
+Check that Crossplane activated only the specified resources:
+<!-- vale Google.WordList = YES -->
+
+```shell
+# Check MRD states - only some should be Active now
+kubectl get mrds \
+  -o jsonpath='{range .items[*]}{.metadata.name}: {.spec.state}{"\n"}{end}' \
+  | grep Active
+# instances.ec2.aws.m.crossplane.io: Active
+# securitygroups.ec2.aws.m.crossplane.io: Active
+# vpcs.ec2.aws.m.crossplane.io: Active
+
+# Verify Crossplane created corresponding CRDs
+kubectl get crds | grep ec2.aws.m.crossplane.io
+# instances.ec2.aws.m.crossplane.io
+# securitygroups.ec2.aws.m.crossplane.io
+# vpcs.ec2.aws.m.crossplane.io
+
+# Count CRDs from EC2 provider - should match activated MRDs
+kubectl get crds | grep ec2.aws.m.crossplane.io | wc -l
+# 3 (only the activated resources)
+```
+
+## Step 6: Measure the impact
+
+Check the significant reduction in resource overhead:
+
+```shell
+# Count CRDs from EC2 provider - should be much lower than 200
+kubectl get crds | grep aws.crossplane.io | wc -l
+# 3 CRDs (99% reduction from 200)
+
+# Calculate memory savings
+echo "197 CRDs saved × 3 MiB = 591 MiB saved (99% reduction)"
+
+# Verify inactive MRDs still exist but consume minimal resources
+kubectl get mrds \
+  -o jsonpath='{.items[?(@.spec.state=="Inactive")]..metadata.name}' | wc -w
+# 197 inactive MRDs (~20 MiB total overhead vs 600 MiB for active CRDs)
+
+# Check total MRDs (active + inactive)
+kubectl get mrds | wc -l
+# 200 total MRDs (3 active, 197 inactive)
+```
+
+The selective activation provides massive resource savings while maintaining
+full capability for the resources you actually use.
+
+## Next steps
+
+- Learn more about
+  [ManagedResourceDefinitions]({{<ref "../managed-resources/managed-resource-definitions">}})
+  for detailed concepts and troubleshooting
+- Explore
+  [ManagedResourceActivationPolicies]({{<ref "../managed-resources/managed-resource-activation-policies">}})
+  for advanced activation strategies and best practices
+- Check the [API reference]({{<ref "../api">}}) for complete schema
+  documentation