init code

.dockerignore

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+.git
+.gitlab-ci.yml
+.vscode

.gitlab-ci.yml

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+stages:
+  - main-build
+
+variables:
+  GIT_DEPTH: "1"
+  CONTAINER_REGISTRY: voxsoft/kube-synchro-scale
+
+Build:
+  stage: main-build
+  image: ezkrg/buildx:latest
+  tags:
+    - docker
+  services:
+    - docker:dind
+  script:
+    - docker login -u $CONTAINER_REGISTRY_USER -p $CONTAINER_REGISTRY_PASSWORD
+    - docker buildx create --name mybuilder --use
+    - docker buildx build --platform linux/arm/v7,linux/arm64/v8,linux/amd64 --push
+        -t ${CONTAINER_REGISTRY}:${CI_COMMIT_BRANCH} .
+  except:
+    - tags
+
+Release:
+  stage: main-build
+  image: ezkrg/buildx:latest
+  tags:
+    - docker
+  services:
+    - docker:dind
+  script:
+    - docker login -u $CONTAINER_REGISTRY_USER -p $CONTAINER_REGISTRY_PASSWORD
+    - docker buildx create --name mybuilder --use
+    - docker buildx build --platform linux/arm/v7,linux/arm64/v8,linux/amd64 --push
+        -t ${CONTAINER_REGISTRY}:${CI_COMMIT_TAG} 
+        -t ${CONTAINER_REGISTRY}:latest .
+  only:
+    - tags

Dockerfile

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+FROM python:3.9-slim
+LABEL maintainer="Oleksii Marchenko <[email protected]>"
+
+WORKDIR /usr/src/app
+COPY . .
+RUN pip3 install -r requirements.txt
+CMD python3 main.py

README.md

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+# kube-synchro-scale
+Publish metrics that allows you to scale 2 Kubernetes Deployments almost synchronously using HPA
+
+## How does it works
+HTTP server gives you an `synchro_scale_coefficient` metric on `/metrics` URL path which represent next formula: `Source Deploy Replicas / Target Deploy Replicas`
+
+## Configuration
+Use environment variables to configure the application
+
+| Environment variable name | Description             | Default value  |
+|:--------------------------|:------------------------|:---------------|
+|`METRIC_PORT`              | Metrics port            | `9102`           | 
+|`METRIC_PATH`              | Metrics URL path        | `/metrics`       |
+|`DEPLOY_SOURCE_NAME`       |Deployment name to be in sync with |      | 
+|`DEPLOY_SOURCE_NAMESPACE`  |Deployment namespace to be in sync with|  | 
+|`DEPLOY_TARGET_NAME`       |Deployment name to be synced    |         |
+|`DEPLOY_TARGET_NAMESPACE`  |Deployment namespace to be synced   |     |
+
+## Required permissions
+- List and Get Deployments
+
+## Example usage
+Minimal setup (Permissions and prometheus configuration not included)
+```yaml
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: targetapp
+spec:
+  selector:
+    matchLabels:
+      app: targetapp
+  template:
+    metadata:
+      labels:
+        app: targetapp
+      annotations:
+        prometheus.io/scrape: "true"
+        prometheus.io/path: /metrics
+        prometheus.io/port: '9102'
+    spec:
+      containers:
+        - name: kube-synchro-scale
+          image: voxsoft/kube-synchro-scale:1.0.0
+          imagePullPolicy: Always
+          ports:
+            - containerPort: 9102
+              protocol: TCP
+          env:
+            - name: DEPLOY_SOURCE_NAME
+              value: sourceapp
+            - name: DEPLOY_SOURCE_NAMESPACE
+              value: default
+            - name: DEPLOY_TARGET_NAME
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.name
+            - name: DEPLOY_TARGET_NAMESPACE
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.namespace
+
+---
+apiVersion: autoscaling/v2beta2
+kind: HorizontalPodAutoscaler
+metadata:
+  name: scale-targetapp-based-on-sourceapp-replicas
+spec:
+  scaleTargetRef:
+    apiVersion: apps/v1
+    kind: Deployment
+    name: targetapp
+  minReplicas: 1
+  maxReplicas: 10
+  metrics:
+    - type: Pods
+      pods:
+        metric:
+          name: synchro_scale_coefficient
+        target:
+          type: AverageValue
+          averageValue: 1000m
+```
+
+Other examples [./examples](./examples)

examples/complex.yaml

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+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: kube-synchro-scale
+  namespace: default
+
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: kube-synchro-scale
+  namespace: default
+rules:
+- apiGroups: [ "apps" ]
+  resources: [ "deployments" ]
+  verbs: ["list", "get"]
+
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: kube-synchro-scale
+  namespace: default
+subjects:
+- kind: ServiceAccount
+  name: kube-synchro-scale
+  namespace: default
+roleRef:
+  kind: Role
+  name: kube-synchro-scale
+  apiGroup: rbac.authorization.k8s.io
+
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: targetapp
+  namespace: default
+spec:
+  selector:
+    matchLabels:
+      app: targetapp
+  template:
+    metadata:
+      labels:
+        app: targetapp
+      annotations:
+        prometheus.io/scrape: "true"
+        prometheus.io/path: /metrics
+        prometheus.io/port: '9102'
+    spec:
+      automountServiceAccountToken: true
+      serviceAccountName: kube-synchro-scale
+      containers:
+        # - Your other containers
+        - name: kube-synchro-scale
+          image: voxsoft/kube-synchro-scale:develop
+          imagePullPolicy: Always
+          resources: {}
+          ports:
+            - containerPort: 9102
+              protocol: TCP
+          env:
+            - name: DEPLOY_SOURCE_NAME
+              value: sourceapp
+            - name: DEPLOY_SOURCE_NAMESPACE
+              value: default
+            - name: DEPLOY_TARGET_NAME
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.name
+            - name: DEPLOY_TARGET_NAMESPACE
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.namespace
+
+---
+apiVersion: autoscaling/v2beta2
+kind: HorizontalPodAutoscaler
+metadata:
+  name: scale-targetapp-based-on-sourceapp-replicas
+  namespace: default
+spec:
+  scaleTargetRef:
+    apiVersion: apps/v1
+    kind: Deployment
+    name: targetapp
+  minReplicas: 1
+  maxReplicas: 10
+  metrics:
+    - type: Pods
+      pods:
+        metric:
+          name: synchro_scale_coefficient
+        target:
+          type: AverageValue
+          averageValue: 1000m
+  behavior:
+    scaleUp:
+      stabilizationWindowSeconds: 60
+      policies:
+      - type: Percent
+        value: 100
+        periodSeconds: 15
+    scaleDown:
+      stabilizationWindowSeconds: 60
+      policies:
+      - type: Percent
+        value: 100
+        periodSeconds: 15

main.py

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+from kubernetes import client, config, watch
+from http.server import BaseHTTPRequestHandler, HTTPServer
+from os import environ
+
+metric_port = environ.get('METRIC_PORT', '9102')
+metric_path = environ.get('METRIC_PATH', '/metrics')
+deploy_source_name      = environ.get('DEPLOY_SOURCE_NAME')
+deploy_source_namespace = environ.get('DEPLOY_SOURCE_NAMESPACE')
+deploy_target_name      = environ.get('DEPLOY_TARGET_NAME')
+deploy_target_namespace = environ.get('DEPLOY_TARGET_NAMESPACE')
+
+def metric_value():
+    try:
+        config.load_incluster_config()
+    except:
+        print("ERROR: Incluster config load failed. Loading local kube config. If you see this in cluster check Pod permissions")
+        config.load_kube_config()
+    v1 = client.AppsV1Api()
+    deploy_source = v1.list_namespaced_deployment(deploy_source_namespace, field_selector = f"metadata.name={deploy_source_name}")
+    deploy_target = v1.list_namespaced_deployment(deploy_target_namespace, field_selector = f"metadata.name={deploy_target_name}")
+    return deploy_source.items[0].status.replicas / deploy_target.items[0].status.replicas
+
+class handler(BaseHTTPRequestHandler):
+    def do_GET(self):
+        if self.path == metric_path:
+            self.send_response(200)
+            self.send_header('Content-type','text/html')
+            self.end_headers()
+            message = "synchro_scale_coefficient" + " " + str(metric_value())
+            self.wfile.write(bytes(message, "utf8"))
+        else:
+            self.send_response(404)
+
+with HTTPServer(('', int(metric_port)), handler) as server:
+    server.serve_forever()

requirements.txt

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+kubernetes