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Leases

A lease represents ownership with a limited lifetime.

It allows a client to control a resource safely, even in the presence of failures.

The Core Idea​

A lease provides:

Exclusive ownership + automatic expiration
  • Ownership ensures only one client controls a resource
  • Expiration ensures the system recovers if the owner fails

Why Leases Exist​

In distributed systems:

  • Processes can crash
  • Machines can go down
  • Network connections can be lost

Without leases:

  • Resources may remain locked forever
  • Systems can become inconsistent

Leases solve this by introducing time-bound ownership.

How a Lease Works​

A lease follows a lifecycle:

Acquire → Active → Renew (optional) → Expire → Released

1. Acquire​

  • A client acquires a lease for a duration
  • The lease becomes active immediately

2. Active​

  • The client owns the lease
  • It can safely perform operations

3. Renew (Optional)​

  • The client can extend the lease before expiration
  • This resets the expiration timer

4. Expire​

  • If not renewed, the lease expires automatically
  • Ownership is released

5. Released​

  • Other clients can acquire the lease

Example Scenario​

A background worker processes jobs:

  • Worker A acquires a lease
  • It processes tasks
  • If Worker A crashes, the lease expires
  • Worker B takes over

No manual cleanup is required.

Binding Keys to Leases​

Keys can be associated with a lease.

  • The key exists only while the lease is active
  • When the lease expires, associated keys are cleaned up automatically

This is useful for:

  • Temporary ownership
  • Resource tracking
  • Distributed coordination

Failure & Expiry Behavior​

Leases are designed to handle failure safely:

  • If a client crashes → lease expires
  • If a network is lost → lease expires
  • If renewal stops → lease expires

The system guarantees that:

  • Ownership is eventually released
  • No stale ownership remains

Lease vs Lock​

Leases are similar to locks, but safer:

  • Lock → ownership until explicitly released
  • Lease → ownership with automatic expiry

This prevents deadlocks caused by failures.

Key Characteristics​

  • Time-bound ownership
  • Automatic cleanup
  • Exclusive access
  • Distributed-safe behavior

Why Leases Matter​

Leases allow you to build systems that are:

  • Reliable
  • Self-healing
  • Safe under failure

They are a foundational primitive for coordination.

What’s Next​

👉 Continue to Coordination Model to see how leases enable locks, counters, and watch