Prevent lease explosions
As your Vault environment scales to meet deployment needs, you run the risk of lease explosions. Lease explosions can occur when a Vault cluster is over-subscribed and clients overwhelm system resources with consistent, high-volume API requests
Unchecked lease explosions create a memory drain on the active node, which can cascade to other nodes and result in denial-of-service issues for the entire cluster.
Look for early warning signs
Cleaning up after a lease explosion is time consuming and resource intensive, so we strongly recommend monitoring your Vault instance for signals that your Vault deployment has matured and requires tuning:
| Issue | Possible cause |
|---|---|
| Unused leases consume storage space for extended periods while waiting to expire | The TTL values for dynamic secret leases or authentication tokens may be too high |
| Lease revocation fails frequently | Failures in an external service (e.g., for dynamic secrets) |
| Build up of leases associated with unused credentials | Clients are not reusing valid, existing leases |
| Lease revocation is slow | Insufficient IOPS for the storage backend |
| Rapid lease count growth disproportionate to the number of clients | Misconfiguration or anti-patterns in client usage |
Enforce client best practices
High lease counts can degrade system performance:
- Use the smallest default time-to-live (TTL) possible for tokens and leases to avoid excessive unexpired lease backlogs and high-volume, simultaneous expirations.
- Review telemetry for aberrant client behavior that might lead to rapid over-subscription.
- Limit the number of simultaneous dynamic secret requests and service token authentication requests.
- Ensure that machine clients adhere to recommended AppRole patterns.
- Review AppRole best practices.
Set reasonable TTL guardrails
Choose appropriate defaults for your situation and use resource quotas as guardrails against lease explosion. You can set default and maximum TTLs globally, in the mount configuration for a specific authN or secrets plugin, and at the role-level (e.g., database credential roles).
Vault prioritizes TTL values by granularity:
- Global values act as the default.
- Plugin TTL values override global values.
- Role, group, and user level TTL values override plugin and global values.
TTL changes are not retroactive
Leases and tokens keep the TTL value in affect during their creation. When you adjust TTL values, the new limits only apply to leases and tokens issued after you deploy the changes.
Monitor key metrics and logs
Proactive monitoring is key to finding problematic behavior and usage patterns before they escalate:
- Review key Vault metrics
- Understand metric anti-patterns
- Monitor Vault audit device logs for quota-related failures.
Control resource usage with quotas
Use API rate limiting quotas and lease count quotas to limit the number of leases generated on a per-mount basis and control resource consumption for your Vault instance where hard limits makes sense.
Consider batch tokens
If your environment inherently leads to a large number of lease requests, consider using batch tokens over service tokens.
The following resources can help you decide if batch tokens are reasonable for your situation:
Next steps
Proactive monitoring and periodic usage analysis can help you identify potential problems before they escalate.
- Brush up on general Vault resource quotas in general.
- Learn about lease count quotas for Vault Enterprise.
- Learn how to query audit device logs.
- Review recommended Vault lease limits.
- Review lease anti-patterns for a clear explanation of the issue and solution.