diff --git a/.changeset/sixty-eggs-cheat.md b/.changeset/sixty-eggs-cheat.md
new file mode 100644
index 0000000000..f1d68eef8a
--- /dev/null
+++ b/.changeset/sixty-eggs-cheat.md
@@ -0,0 +1,5 @@
+---
+"@guardian/cdk": patch
+---
+
+feat(experimental-ec2-pattern): Tag launch template to improve observability
diff --git a/src/constants/metadata-keys.ts b/src/constants/metadata-keys.ts
index 55f88de8d0..520937024c 100644
--- a/src/constants/metadata-keys.ts
+++ b/src/constants/metadata-keys.ts
@@ -4,4 +4,5 @@ export const MetadataKeys = {
   REPOSITORY_NAME: "gu:repo",
   LOG_KINESIS_STREAM_NAME: "LogKinesisStreamName",
   SYSTEMD_UNIT: "SystemdUnit",
+  BUILD_IDENTIFIER: "gu:build-identifier",
 };
diff --git a/src/constructs/autoscaling/asg.ts b/src/constructs/autoscaling/asg.ts
index bd7aaaedcc..2bbfab1281 100644
--- a/src/constructs/autoscaling/asg.ts
+++ b/src/constructs/autoscaling/asg.ts
@@ -80,6 +80,9 @@ export class GuAutoScalingGroup extends GuAppAwareConstruct(AutoScalingGroup) {
   public readonly amiParameter: GuAmiParameter;
   public readonly imageRecipe?: string | AmigoProps;
 
+  // Sadly this cannot be named `launchTemplate` as it would clash with a private property on the `AutoScalingGroup` class
+  public readonly instanceLaunchTemplate: LaunchTemplate;
+
   constructor(scope: GuStack, id: string, props: GuAutoScalingGroupProps) {
     const {
       app,
@@ -162,6 +165,7 @@ export class GuAutoScalingGroup extends GuAppAwareConstruct(AutoScalingGroup) {
     this.app = app;
     this.amiParameter = imageId;
     this.imageRecipe = imageRecipe;
+    this.instanceLaunchTemplate = launchTemplate;
 
     targetGroup && this.attachToApplicationTargetGroup(targetGroup);
 
diff --git a/src/experimental/patterns/__snapshots__/ec2-app.test.ts.snap b/src/experimental/patterns/__snapshots__/ec2-app.test.ts.snap
index 5626d49f49..cd9e9ce9f7 100644
--- a/src/experimental/patterns/__snapshots__/ec2-app.test.ts.snap
+++ b/src/experimental/patterns/__snapshots__/ec2-app.test.ts.snap
@@ -841,6 +841,10 @@ exports[`The GuEc2AppExperimental pattern matches the snapshot 1`] = `
                   "Key": "App",
                   "Value": "test-gu-ec2-app",
                 },
+                {
+                  "Key": "gu:build-identifier",
+                  "Value": "TEST",
+                },
                 {
                   "Key": "gu:cdk:version",
                   "Value": "TEST",
@@ -870,6 +874,10 @@ exports[`The GuEc2AppExperimental pattern matches the snapshot 1`] = `
                   "Key": "App",
                   "Value": "test-gu-ec2-app",
                 },
+                {
+                  "Key": "gu:build-identifier",
+                  "Value": "TEST",
+                },
                 {
                   "Key": "gu:cdk:version",
                   "Value": "TEST",
@@ -937,7 +945,7 @@ dpkg -i /test-gu-ec2-app/test-gu-ec2-app-123.deb
                   "         --targets Id=$INSTANCE_ID,Port=9000         --query "TargetHealthDescriptions[0].TargetHealth.State")
 
       until [ "$STATE" == "\\"healthy\\"" ]; do
-        echo "Instance not yet healthy within target group. Current state $STATE. Sleeping..."
+        echo "Instance running build TEST not yet healthy within target group. Current state $STATE. Sleeping..."
         sleep 5
         STATE=$(aws elbv2 describe-target-health           --target-group-arn ",
                   {
@@ -950,7 +958,7 @@ dpkg -i /test-gu-ec2-app/test-gu-ec2-app-123.deb
                   "           --targets Id=$INSTANCE_ID,Port=9000           --query "TargetHealthDescriptions[0].TargetHealth.State")
       done
 
-      echo "Instance is healthy in target group."
+      echo "Instance running build TEST is healthy in target group."
       
 # GuEc2AppExperimental UserData End",
                 ],
@@ -966,6 +974,10 @@ dpkg -i /test-gu-ec2-app/test-gu-ec2-app-123.deb
                 "Key": "App",
                 "Value": "test-gu-ec2-app",
               },
+              {
+                "Key": "gu:build-identifier",
+                "Value": "TEST",
+              },
               {
                 "Key": "gu:cdk:version",
                 "Value": "TEST",
diff --git a/src/experimental/patterns/ec2-app.test.ts b/src/experimental/patterns/ec2-app.test.ts
index 676f3695ee..b687443ddb 100644
--- a/src/experimental/patterns/ec2-app.test.ts
+++ b/src/experimental/patterns/ec2-app.test.ts
@@ -62,6 +62,7 @@ describe("The GuEc2AppExperimental pattern", () => {
       scaling: {
         minimumInstances: 1,
       },
+      buildIdentifier: "TEST",
     };
   }
 
diff --git a/src/experimental/patterns/ec2-app.ts b/src/experimental/patterns/ec2-app.ts
index a028264c2c..ea41fe1f4b 100644
--- a/src/experimental/patterns/ec2-app.ts
+++ b/src/experimental/patterns/ec2-app.ts
@@ -1,9 +1,10 @@
 import type { IAspect } from "aws-cdk-lib";
-import { Aspects, CfnParameter, Duration } from "aws-cdk-lib";
+import { Aspects, CfnParameter, Duration, Tags } from "aws-cdk-lib";
 import { CfnAutoScalingGroup, CfnScalingPolicy, ScalingProcess, UpdatePolicy } from "aws-cdk-lib/aws-autoscaling";
 import type { CfnPolicy } from "aws-cdk-lib/aws-iam";
 import { Effect, Policy, PolicyStatement } from "aws-cdk-lib/aws-iam";
 import type { IConstruct } from "constructs";
+import { MetadataKeys } from "../../constants";
 import { GuAutoScalingGroup } from "../../constructs/autoscaling";
 import type { GuStack } from "../../constructs/core";
 import type { GuEc2AppProps } from "../../patterns";
@@ -234,7 +235,16 @@ class AsgRollingUpdatePolicy extends Policy {
   }
 }
 
-export interface GuEc2AppExperimentalProps extends Omit<GuEc2AppProps, "updatePolicy"> {}
+export interface GuEc2AppExperimentalProps extends Omit<GuEc2AppProps, "updatePolicy"> {
+  /**
+   * Which application build to run.
+   * This will typically match the build number provided by CI.
+   *
+   * @example
+   * process.env.GITHUB_RUN_NUMBER
+   */
+  buildIdentifier: string;
+}
 
 /**
  * An experimental pattern to instantiate an EC2 application that is updated entirely via CloudFormation.
@@ -273,7 +283,7 @@ export interface GuEc2AppExperimentalProps extends Omit<GuEc2AppProps, "updatePo
 export class GuEc2AppExperimental extends GuEc2App {
   constructor(scope: GuStack, props: GuEc2AppExperimentalProps) {
     const { minimumInstances, maximumInstances = minimumInstances * 2 } = props.scaling;
-    const { applicationPort } = props;
+    const { applicationPort, buildIdentifier } = props;
     const { region, stackId } = scope;
 
     super(scope, {
@@ -334,7 +344,7 @@ export class GuEc2AppExperimental extends GuEc2App {
         --query "TargetHealthDescriptions[0].TargetHealth.State")
 
       until [ "$STATE" == "\\"healthy\\"" ]; do
-        echo "Instance not yet healthy within target group. Current state $STATE. Sleeping..."
+        echo "Instance running build ${buildIdentifier} not yet healthy within target group. Current state $STATE. Sleeping..."
         sleep ${RollingUpdateDurations.sleep.toSeconds()}
         STATE=$(aws elbv2 describe-target-health \
           --target-group-arn ${targetGroup.targetGroupArn} \
@@ -343,7 +353,7 @@ export class GuEc2AppExperimental extends GuEc2App {
           --query "TargetHealthDescriptions[0].TargetHealth.State")
       done
 
-      echo "Instance is healthy in target group."
+      echo "Instance running build ${buildIdentifier} is healthy in target group."
       `,
       `# ${GuEc2AppExperimental.name} UserData End`,
     );
@@ -357,6 +367,11 @@ export class GuEc2AppExperimental extends GuEc2App {
         `,
     );
 
+    // If https://github.com/guardian/devx-logs is used, this tag will be added as a marker to logs in Central ELK.
+    Tags.of(autoScalingGroup.instanceLaunchTemplate).add(MetadataKeys.BUILD_IDENTIFIER, buildIdentifier, {
+      applyToLaunchedInstances: true,
+    });
+
     // TODO Once out of experimental, instantiate these `Aspect`s directly in `GuStack`.
     Aspects.of(scope).add(AutoScalingRollingUpdateTimeout.getInstance(scope));
     Aspects.of(scope).add(HorizontallyScalingDeploymentProperties.getInstance(scope));
diff --git a/src/riff-raff-yaml-file/index.test.ts b/src/riff-raff-yaml-file/index.test.ts
index 3b9a33748d..cee641bddc 100644
--- a/src/riff-raff-yaml-file/index.test.ts
+++ b/src/riff-raff-yaml-file/index.test.ts
@@ -1365,6 +1365,7 @@ describe("The RiffRaffYamlFile class", () => {
           },
           applicationPort: 9000,
           imageRecipe: "arm64-bionic-java11-deploy-infrastructure",
+          buildIdentifier: "TEST",
         });
       }
     }