EventBridge — endpoint support

AWS docs: EventBridge API Reference

EventBridge accepts AWS JSON 1.1 via X-Amz-Target: AWSEvents.<operation>. It also accepts Smithy RPC v2 CBOR at /service/EventBridge/operation/<operation> with Smithy-Protocol: rpc-v2-cbor and Content-Type: application/cbor. Overcast implements event buses, rules, targets, tagging, event ingestion, and same-process target delivery.

[!WARNING] Emulation tier: Partial — EventBridge matches common event patterns and fans matched events out to Lambda, SQS, SNS, Step Functions, Kinesis, Firehose and EventBridge event bus targets; scheduled rules can also invoke ECS/Fargate RunTask targets. Target types outside that list, archives/replay, API destinations and advanced pattern operators (prefix, numeric, anything-but, …) are still incomplete.

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Notes

• Target fan-out. PutEvents evaluates exact-match rule patterns and delivers matching events to every target type listed above. A target ARN naming any other service is rejected by PutTargets with a FailedEntries entry carrying ErrorCode: UnsupportedTargetType, rather than being accepted and silently dropped at delivery time. This is a deliberate divergence from AWS, where all ~20 target types work: an honest refusal is preferred to a rule that provisions cleanly and never fires.

• Input transformation. Input, InputPath and InputTransformer are applied before delivery, and a target may set at most one of them (as on AWS). InputPath and InputTransformer.InputPathsMap accept the JSONPath subset AWS uses: $, dotted member access and array indexing. InputTransformer templates may reference <aws.events.rule-name>, <aws.events.rule-arn>, <aws.events.event.json> and <aws.events.event.ingestion-time>.

• Event bus targets. A rule may target another event bus. The event is republished there through PutEvents carrying the original source, detail-type, detail and resources, so a rule on the downstream bus can match on the fields a real rule filters on. A target that sets Input, InputPath or InputTransformer replaces the forwarded detail with the transformed payload and keeps the routing fields. Every hop is a nested in-process call, so a chain is capped at 4 hops: a cycle of buses forwarding to each other terminates with a delivery error naming the hop budget rather than exhausting the stack.

• Retries and dead-letter queues. A failed delivery is retried up to the target’s RetryPolicy.MaximumRetryAttempts (capped at 5 retries) and stops early once the event is older than RetryPolicy.MaximumEventAgeInSeconds, measured from the envelope’s own time. The event is then sent to the target’s DeadLetterConfig SQS queue if one is configured, and otherwise dropped with a logged warning. Retries are immediate: real EventBridge backs off over up to 24 hours, which a synchronous emulator has nowhere to wait for — so in practice the age limit only bites when a target itself is slow to fail.

• Delivery visibility. Recent per-target outcomes (delivered / retried / dead-lettered / dropped) are exposed to the web console at GET /_overcast/eventbridge/deliveries, and each rule’s targets with their resolved type at GET /_overcast/eventbridge/rule-targets. Both are emulator-only console endpoints, not AWS APIs, and the outcome feed is a bounded in-memory ring that does not survive a restart.

• Scheduled ECS targets. Rate and AWS cron expressions are evaluated by an in-process clock-driven engine. ECS/Fargate targets call ECS RunTask with the configured target parameters.

• Cron expressions. The full six-field AWS syntax is supported, shared with EventBridge Scheduler: numbers, , lists, - ranges, / steps (including over a range, 0-6/2), the three-letter month and day names (JAN, MON-FRI, case-insensitive), and the L, LW, <day>W, <day>L and <day>#<n> day specifiers. Day-of-week is AWS’s 1-7 from Sunday, not Go’s 0-6 from Sunday, so 1 is Sunday and 7 is Saturday.

  PutRule refuses an expression it cannot honour rather than storing a rule that would never fire, and the error names the expression and the field at fault. The five-field Unix form is the common mistake and AWS refuses it too — every five minutes is cron(*/5 * * * ? *), not cron(*/5 * * * *).

• Service-originated events. A handful of emulated services publish their own events onto the default bus, the way real AWS services do on a customer’s behalf: CloudWatch alarms (CloudWatch Alarm State Change, every transition), S3 (Object Created / Object Deleted, when a bucket’s EventBridgeConfiguration is set), EC2 (EC2 Instance State-change Notification, every time an instance’s state changes — including its first transition into pending), ECS (ECS Task State Change, every time a task’s lastStatus changes), and Step Functions (Step Functions Execution Status Change, source aws.states, every time a standard-workflow execution’s status changes — RUNNING on start, then SUCCEEDED, FAILED, TIMED_OUT or ABORTED on completion; the FAILED/TIMED_OUT detail carries the execution’s error/cause). Real AWS emits substantially more service-originated events than these five; a rule matching one of those will never fire here — see #758 (closed out by #1225 and #1221).

• Synthetic default bus. DescribeEventBus returns a synthetic “default” bus even if one has not been explicitly created.

• CDK compatible management plane. Sufficient for CDK deployments that create buses, rules, and targets, including scheduled ECS/Fargate task target metadata.

Summary

Category	✅ Supported	❌ Unsupported
Event buses	4
Rules	7
Targets	3
Events	1
Tags	3
Archives		4
Replays		3
Connections		4

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Endpoints

Event buses

Operation	Status	Notes	AWS Docs
CreateEventBus	✅ Supported	Creates a custom event bus	docs
DescribeEventBus	✅ Supported	Returns bus details; synthetic default bus	docs
ListEventBuses	✅ Supported	Always includes default bus	docs
DeleteEventBus	✅ Supported		docs

Rules

Operation	Status	Notes	AWS Docs
PutRule	✅ Supported	Creates or updates a rule	docs
DescribeRule	✅ Supported		docs
ListRules	✅ Supported	Lists rules for a bus	docs
EnableRule	✅ Supported	Sets rule state to ENABLED	docs
DisableRule	✅ Supported	Sets rule state to DISABLED	docs
DeleteRule	✅ Supported		docs
TestEventPattern	✅ Supported	Evaluates an event against a pattern with the matcher rule delivery uses; unparseable patterns are InvalidEventPatternException, mandatory envelope fields are not enforced	docs

Targets

Operation	Status	Notes	AWS Docs
PutTargets	✅ Supported	Adds Lambda, SQS, SNS, Step Functions, Kinesis, Firehose and ECS targets; rejects other target types at add time	docs
ListTargetsByRule	✅ Supported	Lists targets including input transformers and ECS/Kinesis/SQS target parameters	docs
RemoveTargets	✅ Supported	Removes targets from a rule	docs

Events

Operation	Status	Notes	AWS Docs
PutEvents	✅ Supported	Delivers matching rules to Lambda, SQS, SNS, Step Functions, Kinesis and Firehose targets, applying InputPath/InputTransformer and RetryPolicy/DLQ	docs

Tags

Operation	Status	Notes	AWS Docs
TagResource	✅ Supported	Tag buses and rules	docs
ListTagsForResource	✅ Supported	List tags for a resource	docs
UntagResource	✅ Supported	Removes tags from a resource	docs

Archives

Operation	Status	Notes	AWS Docs
CreateArchive	❌ Unsupported	Returns 501	docs
DescribeArchive	❌ Unsupported	Returns 501	docs
ListArchives	❌ Unsupported	Returns 501	docs
DeleteArchive	❌ Unsupported	Returns 501	docs

Replays

Operation	Status	Notes	AWS Docs
StartReplay	❌ Unsupported	Returns 501	docs
DescribeReplay	❌ Unsupported	Returns 501	docs
ListReplays	❌ Unsupported	Returns 501	docs

Connections

Operation	Status	Notes	AWS Docs
CreateConnection	❌ Unsupported	Returns 501	docs
DescribeConnection	❌ Unsupported	Returns 501	docs
ListConnections	❌ Unsupported	Returns 501	docs
DeleteConnection	❌ Unsupported	Returns 501	docs