From 1ccd9038d19efbda739b1b19312b232b01d6a97e Mon Sep 17 00:00:00 2001
From: Alexander Thaller <alexander@thaller.ws>
Date: Wed, 22 Nov 2023 10:56:30 +0100
Subject: [PATCH] Implement updates of deployment when echo changes

Implements updating the replicas field for the deployment when the
accociated echo resource gets updated.
---
 echo-example.yaml |  2 +-
 src/echo.rs       | 28 +++++++++++++++++++++++++++-
 src/main.rs       | 41 +++++++++++++++++++++++++++++++++--------
 3 files changed, 61 insertions(+), 10 deletions(-)

diff --git a/echo-example.yaml b/echo-example.yaml
index 39493a2..e2153b5 100644
--- a/echo-example.yaml
+++ b/echo-example.yaml
@@ -5,4 +5,4 @@ metadata:
   name: test-echo # Name of the "Echo" custom resource instance, may be changed to your liking
   namespace: default # Namespace must exist and account in KUBECONFIG must have sufficient permissions
 spec:
-  replicas: 2 # Number of "Echo" pods created.
\ No newline at end of file
+  replicas: 2 # Number of "Echo" pods created.
diff --git a/src/echo.rs b/src/echo.rs
index b0b585b..c74458f 100644
--- a/src/echo.rs
+++ b/src/echo.rs
@@ -1,8 +1,9 @@
 use k8s_openapi::api::apps::v1::{Deployment, DeploymentSpec};
 use k8s_openapi::api::core::v1::{Container, ContainerPort, PodSpec, PodTemplateSpec};
 use k8s_openapi::apimachinery::pkg::apis::meta::v1::LabelSelector;
-use kube::api::{DeleteParams, ObjectMeta, PostParams};
+use kube::api::{DeleteParams, ObjectMeta, Patch, PatchParams, PostParams};
 use kube::{Api, Client, Error};
+use serde_json::json;
 use std::collections::BTreeMap;
 
 /// Creates a new deployment of `n` pods with the `inanimate/echo-server:latest` docker image inside,
@@ -68,6 +69,31 @@ pub async fn deploy(
         .await
 }
 
+pub async fn update(
+    client: Client,
+    name: &str,
+    replicas: i32,
+    namespace: &str,
+) -> Result<Deployment, Error> {
+    // Get the existing deployment
+    let deployment_api: Api<Deployment> = Api::namespaced(client, namespace);
+    let patch = json!({
+        "apiVersion": "apps/v1",
+        "kind": "Deployment",
+        "metadata": {
+            "name": name,
+        },
+        "spec": {
+            "replicas": replicas,
+        }
+    });
+    let params = PatchParams::apply("echo-operator").force();
+    let patch = Patch::Apply(&patch);
+    let deployment = deployment_api.patch(name, &params, &patch).await?;
+
+    Ok(deployment)
+}
+
 /// Deletes an existing deployment.
 ///
 /// # Arguments:
diff --git a/src/main.rs b/src/main.rs
index 06de0e6..73f88fb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,7 @@
 use std::sync::Arc;
 
 use futures::stream::StreamExt;
+use k8s_openapi::api::apps::v1::Deployment;
 use kube::runtime::watcher::Config;
 use kube::Resource;
 use kube::ResourceExt;
@@ -69,6 +70,8 @@ enum EchoAction {
     Create,
     /// Delete all subresources created in the `Create` phase
     Delete,
+    /// Update existing subresources to match the desired state
+    Update,
     /// This `Echo` resource is in desired state and requires no actions to be taken
     NoOp,
 }
@@ -94,7 +97,7 @@ async fn reconcile(echo: Arc<Echo>, context: Arc<ContextData>) -> Result<Action,
     let name = echo.name_any(); // Name of the Echo resource is used to name the subresources as well.
 
     // Performs action as decided by the `determine_action` function.
-    return match determine_action(&echo) {
+    match determine_action(context.client.clone(), &echo).await? {
         EchoAction::Create => {
             // Creates a deployment with `n` Echo service pods, but applies a finalizer first.
             // Finalizer is applied first, as the operator might be shut down and restarted
@@ -108,6 +111,7 @@ async fn reconcile(echo: Arc<Echo>, context: Arc<ContextData>) -> Result<Action,
             echo::deploy(client, &name, echo.spec.replicas, &namespace).await?;
             Ok(Action::requeue(Duration::from_secs(10)))
         }
+
         EchoAction::Delete => {
             // Deletes any subresources related to this `Echo` resources. If and only if all subresources
             // are deleted, the finalizer is removed and Kubernetes is free to remove the `Echo` resource.
@@ -123,9 +127,16 @@ async fn reconcile(echo: Arc<Echo>, context: Arc<ContextData>) -> Result<Action,
             finalizer::delete(client, &name, &namespace).await?;
             Ok(Action::await_change()) // Makes no sense to delete after a successful delete, as the resource is gone
         }
+
+        EchoAction::Update => {
+            // Update the deployment to match the desired state
+            echo::update(client, &name, echo.spec.replicas, &namespace).await?;
+            Ok(Action::requeue(Duration::from_secs(10)))
+        }
+
         // The resource is already in desired state, do nothing and re-check after 10 seconds
         EchoAction::NoOp => Ok(Action::requeue(Duration::from_secs(10))),
-    };
+    }
 }
 
 /// Resources arrives into reconciliation queue in a certain state. This function looks at
@@ -134,19 +145,33 @@ async fn reconcile(echo: Arc<Echo>, context: Arc<ContextData>) -> Result<Action,
 ///
 /// # Arguments
 /// - `echo`: A reference to `Echo` being reconciled to decide next action upon.
-fn determine_action(echo: &Echo) -> EchoAction {
-    return if echo.meta().deletion_timestamp.is_some() {
-        EchoAction::Delete
+async fn determine_action(client: Client, echo: &Echo) -> Result<EchoAction, Error> {
+    if echo.meta().deletion_timestamp.is_some() {
+        Ok(EchoAction::Delete)
     } else if echo
         .meta()
         .finalizers
         .as_ref()
         .map_or(true, |finalizers| finalizers.is_empty())
     {
-        EchoAction::Create
+        Ok(EchoAction::Create)
     } else {
-        EchoAction::NoOp
-    };
+        let deployment_api: Api<Deployment> = Api::namespaced(
+            client,
+            echo.meta()
+                .namespace
+                .as_ref()
+                .expect("expected namespace to be set"),
+        );
+
+        let deployment = deployment_api.get(&echo.name_any()).await?;
+
+        if deployment.spec.expect("expected spec to be set").replicas != Some(echo.spec.replicas) {
+            Ok(EchoAction::Update)
+        } else {
+            Ok(EchoAction::NoOp)
+        }
+    }
 }
 
 /// Actions to be taken when a reconciliation fails - for whatever reason.