Design a service discovery system
PremiumDistributed infrastructureEasy
- Service discovery
- Service registry
- Health checks
Quick answer
This distributed infrastructure interview question asks you to design a service discovery system. Aim for a design that keeps working across many machines and failures, then explain partitioning, replication, coordination and trade-offs. Interviewers want to see how you reason about failures, consistency and scale.
The problem
Design a service discovery system that tells every service where the healthy instances of the services it calls are running. Instances register, health checks remove dead ones, and callers get updates within seconds. The hard parts are tracking 60,000 churning instances, pushing changes to 900,000 watchers, and not breaking traffic when the registry fails.
Today addresses are kept in config files, and a deploy that moves instances needs a config change in every caller.
What must a service discovery system do?
- Register and deregister: Instances register with service name, address, port, zone and metadata, and deregister on shutdown.
- Health checks: A local agent on each host checks its instances and reports changes.
How well must it do it?
- Freshness: A new instance is visible to callers within 5 s; a dead one is removed within 15 s.
- Resilience: If the registry is unreachable, callers keep using the last known healthy list.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Service discovery
- Service registry
- Health checks
- Raft
- Watches
- Client side load balancing
How you’ll practise
- Requirements
- Estimate
- Data model and API
- Partitioning and replication
- Consistency and failures
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any distributed infrastructure design round.
- States the consistency and availability guarantees up front
- Explains partitioning and replication choices
- Describes how nodes agree and recover after failures
- Handles network partitions and slow nodes
- Plans for adding and removing capacity safely
- Names the trade-offs instead of hiding them
Questions people ask about this interview question
- Which design type is this question?
- It is a distributed infrastructure question. You design a service discovery system and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Easy, so it suits engineers who are new to distributed infrastructure interviews. It is also a good warm-up before harder questions.
- What should I cover first?
- Start with the guarantees the system must give and the failures it must survive. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team