ECS Health Checks Kept Failing Because curl Was Missing

TL;DR

• The Fargate task definition used curl for health checks, but the base image node:22-alpine did not include curl.
• The command itself failed, so ECS marked tasks as Unhealthy and restarted them in a loop.
• Fixed by installing curl (apk add --no-cache curl) or switching to a check that does not depend on extra packages.

Context

• Infra: ECS (Fargate) + Application Load Balancer
• Container base image: node:22-alpine
• ALB health check: /_health (app returns 204)

ALB health checks were green, but ECS tasks stopped every few minutes with HealthCheck messages in stoppedReason. App logs showed steady GET /_health 204, so HTTP itself seemed fine.

Root Cause

The task definition used this healthCheck.command:

["CMD-SHELL", "curl -f http://127.0.0.1:1337/_health"]

node:22-alpine is a minimal Alpine image and does not include the curl binary. The command failed regardless of the HTTP response, so ECS marked the task Unhealthy and restarted it.

Fastest Recovery

The quickest fix is to install curl in the image. Add this to your Dockerfile and redeploy.

FROM node:22-alpine

RUN apk add --no-cache curl ca-certificates

WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .

EXPOSE 1337
CMD ["npm", "run", "start"]

After deploy, tasks started normally and both ECS/ALB checks turned green.

Prevention and Alternatives

• Avoid extra packages: Node.js 18+ includes fetch, so you can set healthCheck.command to node -e "fetch('http://127.0.0.1:1337/_health').then(res => { if (!res.ok) process.exit(1); }).catch(() => process.exit(1));" without installing curl.
• Create a dedicated health endpoint: Return dependency checks along with HTTP status to speed up incident triage.
• Verify tools during build: Alpine images are small, but design CMD and health checks assuming curl/bash are absent. Document minimal dependencies with apk info -L curl if needed.
• Improve monitoring: Add HealthCheckFailed alarms for Fargate tasks because CloudWatch Logs alone can miss early signals.

Summary

Even if ALB checks pass, ECS will restart tasks if the task-level health check fails. When using minimal images, inventory what is and is not included, and plan for alternatives when required tools are missing.