From d0d2ed85e020dbe6e1295bcfaaebc1ca77a37e9c Mon Sep 17 00:00:00 2001
From: yashdeep <yashdeep@clevertap.com>
Date: Thu, 6 Nov 2025 14:31:53 +0530
Subject: [PATCH 1/2] feat(stack): add spot instance support via
 MixedInstancesPolicy

Add support for EC2 Spot instances in the Auto Scaling Group using
MixedInstancesPolicy. This allows users to configure spot instance
allocation strategy and on-demand capacity settings.

New environment variables:
- SEMAPHORE_AGENT_ON_DEMAND_BASE_CAPACITY: Minimum on-demand instances (default: 0)
- SEMAPHORE_AGENT_ON_DEMAND_PERCENTAGE_ABOVE_BASE: Percentage of on-demand
  instances above base capacity (default: 100)
- SEMAPHORE_AGENT_SPOT_ALLOCATION_STRATEGY: Spot allocation strategy
  (optional, e.g., 'price-capacity-optimized')

The Auto Scaling Group now uses MixedInstancesPolicy instead of a simple
launch template, enabling spot instance support while maintaining backward
compatibility with existing configurations.

Signed-off-by: yashdeep <yashdeep@clevertap.com>
---
 lib/argument-store.js            |  3 +++
 lib/aws-semaphore-agent-stack.js | 33 ++++++++++++++++++++++++++------
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/lib/argument-store.js b/lib/argument-store.js
index 3cc4f79..c4b3118 100644
--- a/lib/argument-store.js
+++ b/lib/argument-store.js
@@ -43,6 +43,9 @@ class ArgumentStore {
     "SEMAPHORE_AGENT_OVERPROVISION_FACTOR": "0",
     "SEMAPHORE_AGENT_USE_IPV6": "false",
     "SEMAPHORE_AGENT_ALLOW_PUBLIC_SUBNET": "false",
+    "SEMAPHORE_AGENT_ON_DEMAND_BASE_CAPACITY": "0",
+    "SEMAPHORE_AGENT_ON_DEMAND_PERCENTAGE_ABOVE_BASE": "100",
+    "SEMAPHORE_AGENT_SPOT_ALLOCATION_STRATEGY": "",
   }
 
   static validOverprovisionStrategies = ["none", "number", "percentage"]
diff --git a/lib/aws-semaphore-agent-stack.js b/lib/aws-semaphore-agent-stack.js
index b18968f..e42179d 100644
--- a/lib/aws-semaphore-agent-stack.js
+++ b/lib/aws-semaphore-agent-stack.js
@@ -470,11 +470,11 @@ class AwsSemaphoreAgentStack extends Stack {
 
   createAutoScalingGroup(launchTemplate) {
     const cfnLaunchTemplate = launchTemplate.node.defaultChild
-    let autoScalingGroup = new CfnAutoScalingGroup(this, 'autoScalingGroup', {
-      launchTemplate: {
-        launchTemplateId: cfnLaunchTemplate.ref,
-        version: cfnLaunchTemplate.attrLatestVersionNumber
-      },
+    const onDemandBaseCapacity = this.argumentStore.get("SEMAPHORE_AGENT_ON_DEMAND_BASE_CAPACITY");
+    const onDemandPercentageAboveBase = this.argumentStore.get("SEMAPHORE_AGENT_ON_DEMAND_PERCENTAGE_ABOVE_BASE");
+    const spotAllocationStrategy = this.argumentStore.get("SEMAPHORE_AGENT_SPOT_ALLOCATION_STRATEGY");
+
+    let autoScalingGroupProps = {
       minSize: this.argumentStore.get("SEMAPHORE_AGENT_ASG_MIN_SIZE"),
       maxSize: this.argumentStore.get("SEMAPHORE_AGENT_ASG_MAX_SIZE"),
       cooldown: "60",
@@ -485,7 +485,28 @@ class AwsSemaphoreAgentStack extends Stack {
           propagateAtLaunch: true
         }
       ],
-    });
+    };
+
+    const instancesDistribution = {
+      onDemandBaseCapacity: onDemandBaseCapacity,
+      onDemandPercentageAboveBaseCapacity: onDemandPercentageAboveBase
+    };
+
+    if (spotAllocationStrategy != "") {
+      instancesDistribution.spotAllocationStrategy = spotAllocationStrategy;
+    }
+
+    autoScalingGroupProps.mixedInstancesPolicy = {
+      instancesDistribution: instancesDistribution,
+      launchTemplate: {
+        launchTemplateSpecification: {
+          launchTemplateId: cfnLaunchTemplate.ref,
+          version: cfnLaunchTemplate.attrLatestVersionNumber
+        }
+      }
+    };
+
+    let autoScalingGroup = new CfnAutoScalingGroup(this, 'autoScalingGroup', autoScalingGroupProps);
 
     const maxInstanceLifetime = this.argumentStore.getAsNumber("SEMAPHORE_AGENT_ASG_MAX_INSTANCE_LIFETIME");
     if (maxInstanceLifetime !== 0) {

From 26b0a756afd29053fd87d773e3eeda3539603be0 Mon Sep 17 00:00:00 2001
From: yashdeep <yashdeep@clevertap.com>
Date: Thu, 6 Nov 2025 14:54:42 +0530
Subject: [PATCH 2/2] converting onDemandBaseCapacity and
 onDemandPercentageAboveBase to numbers

Signed-off-by: yashdeep <yashdeep@clevertap.com>
---
 lib/aws-semaphore-agent-stack.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/aws-semaphore-agent-stack.js b/lib/aws-semaphore-agent-stack.js
index e42179d..e7a0678 100644
--- a/lib/aws-semaphore-agent-stack.js
+++ b/lib/aws-semaphore-agent-stack.js
@@ -470,8 +470,8 @@ class AwsSemaphoreAgentStack extends Stack {
 
   createAutoScalingGroup(launchTemplate) {
     const cfnLaunchTemplate = launchTemplate.node.defaultChild
-    const onDemandBaseCapacity = this.argumentStore.get("SEMAPHORE_AGENT_ON_DEMAND_BASE_CAPACITY");
-    const onDemandPercentageAboveBase = this.argumentStore.get("SEMAPHORE_AGENT_ON_DEMAND_PERCENTAGE_ABOVE_BASE");
+    const onDemandBaseCapacity = this.argumentStore.getAsNumber("SEMAPHORE_AGENT_ON_DEMAND_BASE_CAPACITY");
+    const onDemandPercentageAboveBase = this.argumentStore.getAsNumber("SEMAPHORE_AGENT_ON_DEMAND_PERCENTAGE_ABOVE_BASE");
     const spotAllocationStrategy = this.argumentStore.get("SEMAPHORE_AGENT_SPOT_ALLOCATION_STRATEGY");
 
     let autoScalingGroupProps = {