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Feature Flags and Configuration

Kahuna can store feature flags and runtime configuration with strong consistency, revisions, compare-and-set updates, and historical snapshot reads.

Use a predictable key layout:

config/{environment}/{service}/{name}

Examples:

config/prod/payments/max-refund-amount
config/prod/search/enable-new-ranking

Read a Flag​

KahunaKeyValue flag = await client.GetKeyValue(
    "config/prod/search/enable-new-ranking",
    KeyValueDurability.Persistent
);

bool enabled = flag.Success && flag.ValueAsString() == "true";

Update Safely With Compare Revision​

Read the current revision, then update only if nobody changed it first:

KahunaKeyValue current = await client.GetKeyValue(
    "config/prod/search/enable-new-ranking",
    KeyValueDurability.Persistent
);

KahunaKeyValue updated = await client.TryCompareRevisionAndSetKeyValue(
    "config/prod/search/enable-new-ranking",
    "true",
    compareRevision: current.Revision,
    durability: KeyValueDurability.Persistent
);

if (!updated.Success)
    Console.WriteLine("Flag changed before this update was applied.");

Read Historical Configuration​

Use LastModified from one read as a snapshot anchor:

KahunaKeyValue anchor = await client.GetKeyValue(
    "config/prod/search/enable-new-ranking",
    KeyValueDurability.Persistent
);

List<KahunaKeyValue> configAtAnchor = await client.ScanAllByPrefix(
    "config/prod/search",
    KeyValueDurability.Persistent,
    snapshotMs: anchor.LastModified
);

This is useful during incident review when you need to know which flags and settings were visible at one point in time.

For settings that should be read together, use one bucket:

get by bucket `config/prod/search`

From the .NET client:

List<KahunaKeyValue> settings = await client.GetByBucket(
    "config/prod/search",
    KeyValueDurability.Persistent
);

Operational Notes​

  • Use persistent durability for production configuration.
  • Use compare-revision updates in admin tools to avoid lost updates.
  • Keep values compact and parseable, for example JSON for structured settings.
  • Use snapshot reads during postmortems to reconstruct the exact configuration that was visible at the time.