Sometimes the worst ECS failures aren’t the ones that crash loudly — they’re the ones that fail quietly.
I’ve seen services run “successfully” in ECS while the app inside was broken for hours because no alerts fired and no one was watching the right metrics.

If you’re relying on someone to notice and tell you something’s wrong, you’re playing production roulette.

Here are 3 monitoring & alerting mistakes I’ve seen teams make — and how to avoid them.

1️⃣ No Task-Level Metrics

The Problem:
ECS gives you service-level health, but that doesn’t always tell the full story.
A single task might be spiking CPU, running out of memory, or constantly restarting without ever failing the service as a whole.

Fix:

• Enable CloudWatch Container Insights for ECS.

• Set alarms on per-task CPU and memory usage to catch runaway containers early.

• Monitor task restarts — high restart counts usually mean something’s wrong in the app.

2️⃣ Ignoring ALB Metrics

The Problem:
The ALB knows more about your app’s availability than ECS does — but many teams ignore its metrics.
I’ve caught outages faster by watching ALB’s UnHealthyHostCount than by looking at ECS dashboards.

Fix:

• Create CloudWatch alarms for UnHealthyHostCount and TargetResponseTime.

• Pair them with notifications via SNS to Slack, email, or PagerDuty.

• Don’t just set alerts — test them by intentionally failing a container.

3️⃣ No End-to-End Synthetic Checks

The Problem:
Even if ECS tasks and the ALB are “healthy,” your actual user journey might still be broken — login failing, payment API timing out, etc.
Without synthetic checks, you won’t catch these.

Fix:

• Use a tool like Gatus, Pingdom, or CloudWatch Synthetics to run regular HTTP checks against critical endpoints.

• Include flows that mimic real user actions, not just a /health check.

• Alert if these fail more than once in a short period.

💡 Bonus Tip:
Monitoring is only half the job — alert routing matters just as much.
If an alert triggers at 3 a.m. and goes to the wrong inbox, it might as well not exist.

Final Thought

Good ECS deployments don’t just run well — they tell you when something’s wrong, ideally before users even notice.
Watch the right metrics, test your alerts, and make monitoring part of your deployment checklist.

Now that we’ve covered:
1️⃣ Health checks
2️⃣ Container & image issues
3️⃣ ALB misconfigurations
4️⃣ Networking pitfalls
5️⃣ Monitoring gaps

…you’ve got a solid checklist for avoiding the most common ECS downtime traps.

Sometimes your ECS service isn’t broken — it’s just stranded on the wrong network.
I’ve had deployments where everything “looked” fine in ECS, but the app couldn’t reach the internet, the ALB couldn’t reach the tasks, or database connections failed — all because of networking misconfigurations.

Here are 3 networking mistakes I’ve run into (and fixed) when working with ECS.

1️⃣ Wrong Subnet Placement

The Problem:
If you place your ECS tasks in public subnets without proper security controls, you risk exposure.
On the flip side, if they’re in private subnets without a NAT gateway, they might not reach the internet for updates or API calls.

Fix:

• For internet-facing apps, put the ALB in public subnets and ECS tasks in private subnets.

• Add a NAT gateway so tasks in private subnets can make outbound calls.

• Double-check subnet associations in the ECS service configuration.

2️⃣ Security Group Over-Lockdown

The Problem:
Security groups are great for locking things down, but too much lockdown can block even legitimate traffic.
I’ve seen apps fail because the database’s security group didn’t allow inbound from ECS, or the ALB couldn’t connect to the container port.

Fix:

• Allow ECS tasks to connect to any required databases, caches, or APIs via the right ports.

• Make sure the ALB security group is allowed inbound to the ECS task security group on the container port.

• Use security group IDs instead of IP ranges for cleaner, more secure rules.

3️⃣ Missing Route Table Entries

The Problem:
If the route tables for your subnets aren’t set up correctly, requests can’t reach the ALB — or the tasks can’t talk back.
This can silently break your service without obvious error messages in ECS.

Fix:

• Public subnets should have a route to the internet gateway.

• Private subnets that need outbound internet should have a route to the NAT gateway.

• Use VPC flow logs to debug dropped traffic.

💡 Bonus Tip:
If your ECS service depends on external APIs, always test that outbound calls work in staging before going live.
Networking issues often show up only when you try to integrate with the outside world.

Final Thought

ECS services live and die by their network configuration.
Get subnets, security groups, and route tables right — and you’ll save yourself from some of the most frustrating “it works here, but not there” problems in AWS.

One of the most head-scratching issues I’ve run into is when everything in ECS looks fine, but traffic never reaches your container.
The ALB is up, DNS resolves, and ECS says “running”… yet the site’s dead.

When ECS and the ALB aren’t properly connected, you’re essentially running your service in a black hole.
Here are 3 common ALB–ECS integration mistakes I’ve seen — and how to fix them.

1️⃣ Wrong Target Group Registration

The Problem:
The ECS service has to register its tasks into the right ALB target group.
If you picked the wrong target group ARN in your service definition — or updated the ALB later without updating ECS — your containers might not receive traffic at all.

Fix:

• In the ECS service, check the Load Balancing section and confirm it points to the intended target group.

• Verify the target group actually contains your ECS tasks when they’re running.

• If you have multiple services, make sure each uses a unique target group unless you’re intentionally sharing.

2️⃣ Security Groups Blocking Traffic

The Problem:
Even if ECS and the ALB are wired correctly, mismatched security group rules can silently block requests.
For example, your ECS task’s security group might not allow inbound from the ALB’s security group.

Fix:

• In the ALB’s security group, allow inbound traffic from the internet on ports 80 and 443.

• In the ECS task’s security group, allow inbound from the ALB’s security group, not 0.0.0.0/0.

• Outbound should typically be open so the task can respond to the ALB health check.

3️⃣ Listener & Path Rule Mismatches

The Problem:
If the ALB listener rules don’t match the path your users are requesting, the request may never hit your ECS target group.
I once had /api requests silently drop because the listener was only forwarding /.

Fix:

• Check the ALB listener rules and confirm the paths match your application’s endpoints.

• If in doubt, add a catch-all rule to forward everything to your ECS target group.

• Use the ALB access logs to see what requests are hitting it (or not).

💡 Bonus Tip:
If you ever change ports, paths, or target groups — re-run health checks immediately.
A working config can break instantly after an update if these links aren’t aligned.

Final Thought

ECS and ALB work brilliantly together when properly configured — but a single mismatch can cut off all traffic.
Always check target group registration, security group rules, and listener paths before assuming it’s the app’s fault.

One of the most frustrating ECS issues I’ve dealt with is the dreaded crash loop.
You deploy your service, the task starts… then stops… then starts again… over and over.

No traffic is getting through, your ALB target group is empty, and ECS is burning through restarts like there’s no tomorrow.

Here are 3 common reasons I’ve seen ECS tasks get stuck in a crash loop — and how to fix them.

1️⃣ Bad or Missing Environment Variables

The Problem:
Containers often depend on environment variables for database connections, API keys, or service URLs.
If one is missing or incorrect, your app might fail immediately at startup.

Fix:

• Double-check the environment or secrets section in your ECS task definition.

• Make sure sensitive values are coming from AWS Secrets Manager or SSM Parameter Store — not hardcoded.

• Test locally with the same environment variables to confirm the app boots successfully.

2️⃣ Application Port Mismatch

The Problem:
Your ECS task definition might expose port 8080, but your container is actually listening on 3000 (or vice versa).
The ALB can’t connect, the health check fails, and ECS kills the container.

Fix:

• Make sure the container EXPOSE in the Dockerfile matches the containerPort in the ECS task definition.

• Update your ALB target group to check the correct port.

• If you’re running multiple containers in a task, confirm they’re not fighting over the same port.

3️⃣ Crash on Startup Due to Code Errors

The Problem:
If your application throws an unhandled error at boot (e.g., database unreachable, missing config file), ECS will mark the task as stopped almost instantly.

Fix:

• Use docker run locally with the exact same image you push to ECS.

• Check logs in CloudWatch (/ecs/service-name) for error messages.

• Add proper retry logic in your app for external dependencies so it can survive transient failures.

💡 Bonus Tip:
If you’re stuck, set the ECS service minimum healthy percent to 0 temporarily.
This lets ECS replace all tasks at once — useful for breaking out of a crash loop when all running tasks are broken.

Final Thought

Crash loops are rarely random.
They usually come down to bad configs, mismatched ports, or missing dependencies.
Get into the habit of checking environment variables, ports, and logs first — it’ll save you hours of guesswork.

After nearly 2 years in DevOps, one thing is clear:
A “running” ECS task doesn’t always mean a healthy app.

Early on, I deployed a service to Amazon ECS.
Everything looked perfect — tasks running, console green — until I tried to open the app.
Blank screen. Endless loading. Sometimes a nice 503 or 502 for variety.

That’s when I realized: Health checks aren’t just a tick-box — they’re critical to application reliability.

Over time, I’ve seen (and fixed) the same few issues again and again.
Here are 3 ECS health check mistakes to avoid.

1️⃣ Wrong Health Check Path

The Problem:
If your ALB health check is pointing to / but your app’s real “I’m alive” route is /health, you’re in trouble.
The ALB might think everything’s fine even if the important parts of your app are broken.
In my case, / was returning a redirect, so the ALB marked the service unhealthy and ECS kept restarting it.

Fix:

• Set the target group health check path to a dedicated /health endpoint.

• Make sure /health returns a fast 200 OK without relying on slow upstreams.

• If you have critical dependencies (like a database), include lightweight checks for them too.

2️⃣ Not Allowing for Startup Time

The Problem:
During one deployment, my ALB started checking the new ECS tasks before the app was ready.
The result? It marked them unhealthy almost instantly, ECS killed them, and I ended up in a restart loop.

Fix:

• Increase the health check timeout and healthy threshold to give your app breathing room.

• In Kubernetes terms, think of this like a startup probe — don’t respond to the ALB until you’re ready.

• If the app takes ~30 seconds to start, configure health checks so they won’t fail until at least then.

3️⃣ No Alerts for Unhealthy Targets

The Problem:
Without alerts, your ALB could be quietly flagging unhealthy targets and you’d never know.
This happened to me once, and it took a user report to even realize anything was wrong.

Fix:

• Create a CloudWatch alarm on the UnHealthyHostCount metric.

• Send notifications via SNS to Slack, email, or PagerDuty.

• Test it by breaking a container on purpose and confirming the alert fires.

💡 Bonus Tip:
During rolling updates, bad health check settings can drain old tasks before new ones are ready — leaving the ALB with nothing to route to.
Always test rolling updates in staging with health checks enabled.

Final Thought

Green dashboards can lie.
Real reliability comes from health checks that are:

• Well-configured

• Tested in staging

• Backed by good alerting

So the next time ECS says Running, make sure it actually means Healthy.