Design a distributed lock service
PremiumDistributed infrastructureEasy
- Distributed locks
- Fencing tokens
- Raft
Quick answer
This distributed infrastructure interview question asks you to design a distributed lock service. 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 distributed lock service, similar to the locking that ZooKeeper or etcd provide, that services use to make sure only one worker does a job or writes a resource at a time. The hard parts are deciding who holds a lock when servers crash, and staying correct when a client pauses and does not know its lock has expired.
Today teams use a single cache server for locks. When it restarted last month, two workers both thought they held the same lock and wrote conflicting data.
What must a distributed lock service do?
- Acquire and release: A client acquires a named lock, gets a token back, and releases it when done.
- Automatic expiry: If the holder crashes or loses contact, the lock is freed after its lease expires.
How well must it do it?
- Safety: The service never grants a lock to two clients at once.
- Availability: Keeps working with up to 2 server failures, or the loss of one availability zone.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Distributed locks
- Fencing tokens
- Raft
- Leases
- ZooKeeper
- Linearizability
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 distributed lock service 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