From a4d13ed26c0aed6be4fbfdd7f079d6754003d94f Mon Sep 17 00:00:00 2001
From: Tom van Dinther <39470469+tvandinther@users.noreply.github.com>
Date: Mon, 10 Mar 2025 19:05:43 +0100
Subject: [PATCH 1/2] Init app abstraction

Signed-off-by: Tom van Dinther <39470469+tvandinther@users.noreply.github.com>
---
 app-abstraction/README.md           | 103 ++++++++++++++++++++++
 app-abstraction/app.cue             |  36 ++++++++
 app-abstraction/cue.mod/module.cue  |   4 +
 app-abstraction/platform/main.cue   | 129 ++++++++++++++++++++++++++++
 app-abstraction/platform/policy.cue |   7 ++
 app-abstraction/render              |   3 +
 6 files changed, 282 insertions(+)
 create mode 100644 app-abstraction/README.md
 create mode 100644 app-abstraction/app.cue
 create mode 100644 app-abstraction/cue.mod/module.cue
 create mode 100644 app-abstraction/platform/main.cue
 create mode 100644 app-abstraction/platform/policy.cue
 create mode 100755 app-abstraction/render

diff --git a/app-abstraction/README.md b/app-abstraction/README.md
new file mode 100644
index 0000000..dae4343
--- /dev/null
+++ b/app-abstraction/README.md
@@ -0,0 +1,103 @@
+# Application Abstraction
+
+This pattern shows how you can define an application across several deployment targets (such as development and production environments).
+
+## Concept
+
+The application abstraction uses a unified configuration approach whereby the configuration for all possible states are represented within a shared context. Denoting differing configuration states as *environments*, this has several benefits:
+- A declarative approach to defining environment-specific configuration
+- Enhanced readability of configuration by sticking to CUE's core language design principles
+- The ability to define cross-environment values, e.g. "This value in preprod should be the same in prod"
+- Allows users to compose their abstracted configuration however they want
+
+## Structure
+
+The platform abstractions are defined in [platform](./platform/) under a seperate package. This package can be published within a module and distributed internally within your organisation.
+
+The abstraction user defines their app as shown in [app.cue](./app.cue), with the [render](./render) script showing how you might choose to retrieve the rendered output from the configuration.
+
+### Platform Package
+
+The `platform` package contains two key definitions; `#Deployment`, and `#App`. `#Deployment` defines which deployment targets needs to be defined and how. It also puts these together into a lookup of deployment target to manifest list. `#App` is a union of valid abstractions (in this case, only one called `#WebApp`). A user can choose this abstraction to populate their "desired" state for each deployment target.
+
+## Usage
+
+For example, to retrieve the YAML manifest stream for the preview environment:
+```yaml
+$ ./render preview
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: test-app
+spec:
+  hostnames:
+    - test-app.example-dev.com
+  parentRefs:
+    - name: web-gateway-lb
+  rules:
+    - backendRefs:
+        - name: test-app
+          port: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: test-app
+spec:
+  ports:
+    - protocol: TCP
+      port: 8080
+      targetPort: 8080
+  selector:
+    app.kubernetes.io/name: test-app
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: test-app
+  labels:
+    app.kubernetes.io/name: test-app
+spec:
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: test-app
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: test-app
+    spec:
+      containers:
+        - name: test-app
+          image: my-registry.com/test-app:v3
+          ports:
+            - containerPort: 8080
+          env:
+            - name: DEBUG
+              value: "true"
+          resources:
+            requests:
+              cpu: 1
+              memory: 2Gi
+            limits:
+              memory: 4Gi
+---
+apiVersion: autoscaling/v2
+kind: HorizontalPodAutoscaler
+metadata:
+  name: test-app
+spec:
+  scaleTargetRef:
+    apiVersion: apps/v1
+    kind: Deployment
+    name: test-app
+  minReplicas: 1
+  maxReplicas: 1
+  metrics:
+    - type: Resource
+      resource:
+        name: cpu
+        target:
+          type: Utilization
+          averageUtilization: 0.7
+
+```
diff --git a/app-abstraction/app.cue b/app-abstraction/app.cue
new file mode 100644
index 0000000..12781b3
--- /dev/null
+++ b/app-abstraction/app.cue
@@ -0,0 +1,36 @@
+package app
+
+import "github.com/cue-lang/cue-deployment-patterns/app-abstraction/platform"
+
+platform.#Deployment & {
+    let base = platform.#WebApp & {
+        AppName=name: "test-app"
+        image: {
+            registry: "my-registry.com"
+            name: AppName
+        }
+        AppPort=port: 8080
+        healthCheck: port: AppPort
+        scaling: cpuUtilizationThreshold: 0.7
+    }
+
+    preview: base & {
+        image: tag: "v3"
+        hostname: "test-app.example-dev.com"
+        env: DEBUG: "true"
+        scaling: minReplicas: 1
+    }
+    preprod: base & {
+        image: tag: "v2"
+        hostname: "test-app.example-preprod.com"
+        scaling: prod.scaling
+    }
+    prod: base & {
+        image: tag: "v1"
+        hostname: "test-app.example.com"
+        scaling: {
+            minReplicas: 3
+            maxReplicas: minReplicas * 10
+        }
+    }
+}
diff --git a/app-abstraction/cue.mod/module.cue b/app-abstraction/cue.mod/module.cue
new file mode 100644
index 0000000..c3aaf82
--- /dev/null
+++ b/app-abstraction/cue.mod/module.cue
@@ -0,0 +1,4 @@
+module: "github.com/cue-lang/cue-deployment-patterns/app-abstraction"
+language: {
+	version: "v0.12.0"
+}
diff --git a/app-abstraction/platform/main.cue b/app-abstraction/platform/main.cue
new file mode 100644
index 0000000..58ec136
--- /dev/null
+++ b/app-abstraction/platform/main.cue
@@ -0,0 +1,129 @@
+package platform
+
+#ConstrainedString: string & =~"^[A-Za-z-]{1,253}$"
+#Port: int & >=1024 & <=65535
+
+#Deployment: {
+    preview: #App
+    preprod: #App
+    prod: #App
+
+    let deploymentTargets = {
+        "preview": preview
+        "preprod": preprod
+        "prod": prod
+    }
+
+    for deploymentTargetName, appDefinition in deploymentTargets {
+        let httpRoute = {
+            apiVersion: "gateway.networking.k8s.io/v1"
+            kind: "HTTPRoute"
+            metadata: name: appDefinition.name
+            spec: {
+                hostnames: [appDefinition.hostname]
+                parentRefs: [{name: "web-gateway-lb"}]
+                rules: [{
+                    backendRefs: [{
+                        name: service.metadata.name
+                        port: service.spec.ports[0].port
+                    }]
+                }]
+            }
+        }
+
+        let service = {
+            apiVersion: "v1"
+            kind: "Service"
+            metadata: name: appDefinition.name
+            spec: {
+                ports: [{
+                    protocol: "TCP"
+                    port: appDefinition.port
+                    targetPort: port
+                }]
+                selector: deployment.metadata.labels
+            }
+        }
+
+        let deployment = {
+            apiVersion: "apps/v1"
+            kind: "Deployment"
+            DeploymentMetadata=metadata: {
+                name: appDefinition.name
+                labels: "app.kubernetes.io/name": appDefinition.name
+            }
+            spec: {
+                selector: matchLabels: DeploymentMetadata.labels
+                template: {
+                    metadata: labels: DeploymentMetadata.labels
+                    spec: containers: [{
+                        name: DeploymentMetadata.name
+                        let imageRef = appDefinition.image
+                        image: "\(imageRef.registry)/\(imageRef.name):\(imageRef.tag)"
+                        ports: [{containerPort: appDefinition.port}]
+                        env: [for k, v in appDefinition.env {name: k, value: v}]
+                        resources: {
+                            requests: {
+                                cpu: 1
+                                memory: "2Gi"
+                            }
+                            limits: {
+                                memory: "4Gi"
+                            }
+                        }
+                    }]
+                }
+            }
+        }
+
+        let autoscaler = {
+            apiVersion: "autoscaling/v2"
+            kind: "HorizontalPodAutoscaler"
+            metadata: name: appDefinition.name
+            spec: {
+                scaleTargetRef: {
+                    apiVersion: deployment.apiVersion
+                    kind: deployment.kind
+                    name: deployment.metadata.name
+                }
+                minReplicas: appDefinition.scaling.minReplicas
+                maxReplicas: appDefinition.scaling.maxReplicas
+                metrics: [{
+                    type: "Resource"
+                    resource: {
+                        name: "cpu"
+                        target: {
+                            type: "Utilization"
+                            averageUtilization: appDefinition.scaling.cpuUtilizationThreshold
+                        }
+                    }
+                }]
+            }
+        }
+        
+        manifests: (deploymentTargetName): [httpRoute, service, deployment, autoscaler]
+    }
+}
+
+#App: #WebApp // | #OtherApp
+
+#WebApp: {
+    name: #ConstrainedString
+    image: {
+        registry: string
+        name: #ConstrainedString
+        tag: string
+    }
+    port: #Port
+    env: [EnvName=string]: string
+    hostname: string
+    healthCheck: {
+        path: string | *"/healthz"
+        port: #Port
+    }
+    scaling: {
+        minReplicas: int & >0 //& <=maxReplicas
+        maxReplicas: int & <=999 | *minReplicas //& >=minReplicas 
+        cpuUtilizationThreshold: float & >=0.1 & <=0.95
+    }
+}
diff --git a/app-abstraction/platform/policy.cue b/app-abstraction/platform/policy.cue
new file mode 100644
index 0000000..c5cfc7d
--- /dev/null
+++ b/app-abstraction/platform/policy.cue
@@ -0,0 +1,7 @@
+package platform
+
+#Deployment: {
+    preview: hostname: =~ "example-dev.com$"
+    preprod: hostname: =~ "example-preprod.com$"
+    prod: hostname: =~ "example.com$"
+}
diff --git a/app-abstraction/render b/app-abstraction/render
new file mode 100755
index 0000000..bd9cd19
--- /dev/null
+++ b/app-abstraction/render
@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+CUE_EXPERIMENT=evalv3 cue export -e "yaml.MarshalStream(manifests.$1)" --out text

From 9d11ca53cd47b9b1b1bae869d2452ad9c8cbabaf Mon Sep 17 00:00:00 2001
From: Tom van Dinther <39470469+tvandinther@users.noreply.github.com>
Date: Mon, 10 Mar 2025 19:15:30 +0100
Subject: [PATCH 2/2] Update README to include user requirements for the
 pattern

Signed-off-by: Tom van Dinther <39470469+tvandinther@users.noreply.github.com>
---
 app-abstraction/README.md | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/app-abstraction/README.md b/app-abstraction/README.md
index dae4343..896d2a4 100644
--- a/app-abstraction/README.md
+++ b/app-abstraction/README.md
@@ -10,6 +10,13 @@ The application abstraction uses a unified configuration approach whereby the co
 - The ability to define cross-environment values, e.g. "This value in preprod should be the same in prod"
 - Allows users to compose their abstracted configuration however they want
 
+## User Requirements
+
+- Hide implementation details from users
+- Enforce platform policies on users
+- Support several deployment targets such as pre-prod and prod environments
+- Construct complex configuration with a simplified interface
+
 ## Structure
 
 The platform abstractions are defined in [platform](./platform/) under a seperate package. This package can be published within a module and distributed internally within your organisation.