What are target groups?
A target group is a logical grouping of targets, such as EC2 instances, IP addresses, or Lambda functions, that a load balancer routes requests to, and it defines health check settings and routing rules [citation:1].
A target group is a logical grouping of one or more targets (such as EC2 instances, IP addresses, or Lambda functions) that a load balancer routes requests to. It is the fundamental unit for routing and health checks. When you configure a listener rule on a load balancer, you specify a target group as the destination. The target group also defines the health check settings that the load balancer uses to determine the health of its registered targets [citation:1].
Scenario Questions
- 1
You just launched two new EC2 instances and registered them with a target group, but users are getting 502 errors — what’s the most likely thing you forgot to check?
- 2
How would you add a new EC2 instance to a target group attached to an Application Load Balancer, and what port should you use?
- 3
What happens if you register an instance with a target group using a port that no service is listening on?
- 1
Our application’s traffic spiked during a sale, but the load balancer started returning 503s — the target group shows all instances as healthy. What would you investigate next?
- 2
We deployed a new version of our service and now half the requests are failing — the target group still shows all instances as healthy. What could be going wrong?
- 3
You’re rolling out a canary deployment using two target groups. How do you safely shift traffic between them without dropping requests?
- 1
You’re designing a multi-region failover system using Application Load Balancers and target groups — how do you handle cross-region health checks and avoid flapping during network partitions?
- 2
A target group is experiencing intermittent connection timeouts despite healthy instances — what underlying network or configuration issues might you suspect, and how would you validate them?
- 3
Your team uses Auto Scaling with target groups, but new instances take 90 seconds to become ready. How do you reduce user impact during scale-out events without compromising stability?
- 1
We’re migrating from Classic Load Balancers to Application Load Balancers with target groups across 50+ services — what’s your strategy to avoid downtime, validate routing correctness, and roll back safely?
- 2
How would you design a global traffic routing system using multiple ALBs and target groups across regions, while ensuring compliance with latency SLAs and minimizing cross-region data transfer costs?
- 3
A legacy monolith is being split into microservices, each needing its own target group. How do you manage target group lifecycle, permissions, and monitoring at scale without creating operational debt?
Follow-up Questions
- ❓What happens if an instance in the target group fails health checks?
- ❓How do you ensure new instances are added to the right target group during deployment?
- ❓Can you route traffic to multiple target groups from one load balancer?