Status
Current state: Under Discussion
Discussion thread: https://lists.apache.org/thread/3gvsod6vrq5xb415yf0zs8cxry1lnfzf
JIRA:
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
KIP-133 introduced AlterConfigPolicy
to enforce validations when requesting configuration changes for Kafka entities (e.g. Topics), similar to how KIP-108 introduced policies for Topic creation.
At that time, the AlterConfigs
API included all the configurations to be applied (usually after gathering all the current configurations first using DescribeConfigs
call). This has changed after KIP-339 was introduced. With IncrementalAlterConfigs
, only configurations to be changed are including to the request and changes are calculated on the broker-side.
This current context only enables a very limited type of validations (e.g. config x
cannot not be y
), while most important validations have a dependency between configurations (e.g. if value of a=b
and c=d
then x
cannot be y
). Even further, having some policies available only on creation but not when altering means the effort put to validate on creation is wasted on later changes.
If this KIP is accepted, plugin implementations should be able to apply the same policies on creation and on alter config time.
There has been related KIPs that included this proposal:
- KIP-170: Enhanced TopicCreatePolicy and introduction of TopicDeletePolicy (retired and superseded by KIP-201)
- KIP-201: Rationalising Policy interfaces (called abandoned: https://github.com/apache/kafka/pull/4281#issuecomment-1035154386)
This KIP is intended to reduce the scope of the proposal for extending AlterConfigPolicy, without adding new interfaces.
This KIP borrows parts of KIP-170 discussion. If KIP-201 is resurrected, this changes shouldn't increase complexity of the KIP as it is just another field to map and same migration should apply.
Public Interfaces
1. Extend AlterConfigPolicy.RequestMetadata to include existing configurations:
public interface AlterConfigPolicy extends Configurable, AutoCloseable { class RequestMetadata { private final ConfigResource resource; private final Map<String, String> proposedConfigs; private final Map<String, String> resultingConfigs; public RequestMetadata(ConfigResource resource, Map<String, String> proposedConfigs) { this.resource = resource; this.proposedConfigs = proposedConfigs; this.resultingConfigs = Collections.emptyMap(); } public RequestMetadata(ConfigResource resource, Map<String, String> proposedConfigs, Map<String, String> resultingConfigs) { this.resource = resource; this.proposedConfigs = proposedConfigs; this.resultingConfigs = resultingConfigs; } // ... public Map<String, String> resultingConfigs() { return resultingConfigs; } // ... void validate(RequestMetadata requestMetadata) throws PolicyViolationException; }
Where:
resultingConfigs
includes the altered configurations: existing and proposed configurations merged.proposedConfigs
includes the requested configurations, including null or empty values when configuration is requested to be deleted.
Proposed Changes
Enable Managers to use the new property:
ConfigurationControlManager
ZkAdminManager
existing configurations are already available.
Compatibility, Deprecation, and Migration Plan
- What impact (if any) will there be on existing users?
Existing policy implementations should be safe, as new attribute won't be expected. New policy implementations will have to be deployed on brokers running newer versions including existing configurations.
- If we are changing behavior how will we phase out the older behavior?
Will be phased out naturally by rolling out new versions with the latest API.
- If we need special migration tools, describe them here.
No migration tools needed.
- When will we remove the existing behavior?
Behavior is extended, not replaced.
Test Plan
Extending existing AlterConfigPolicy
tests.
Rejected Alternatives
If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.
Reuse configs value to include all resulting configurations
This would be a breaking change on behavior as existing plugins may be expecting only changing configurations.