EventBridge — Amazon EventBridge
Quick start, the eight target types delivery reaches, input shaping, retries and dead-lettering, and which event-pattern match types a rule can filter on.
Buses, rules and targets, with matched events delivered in-process to eight target types, filtered by every event-pattern match type bar three.
Status: ⚠️ Partial
Quick start
Route an event to an SQS queue:
export AWS_ENDPOINT_URL=http://localhost:4566
QUEUE=$(aws sqs create-queue --queue-name orders --query QueueUrl --output text)
ARN=$(aws sqs get-queue-attributes --queue-url "$QUEUE" \
--attribute-names QueueArn --query Attributes.QueueArn --output text)
aws events put-rule --name orders --event-pattern '{"source":["app.orders"]}'
aws events put-targets --rule orders --targets "Id=1,Arn=$ARN"
aws events put-events --entries \
'[{"Source":"app.orders","DetailType":"OrderPlaced","Detail":"{\"id\":1}"}]'
aws sqs receive-message --queue-url "$QUEUE"Any credentials work; with none configured, run eval "$(overcast env)" first
— see Using AWS SDKs and CLI.
What works
| Area | Behaviour |
|---|---|
| Buses and rules | Bus, rule, target and tag CRUD. CreateEventBus stores Description, DeadLetterConfig and KmsKeyIdentifier; DescribeEventBus answers for default whether or not it was created. |
| Bus permissions | PutPermission grants a statement, individually or as a whole Policy document that replaces the bus’s policy; RemovePermission revokes one by StatementId or clears the policy with RemoveAllPermissions. DescribeEventBus reports the result as Policy. Stored, not enforced — like the rest of Overcast’s IAM policies, nothing consults it to authorize a cross-account PutEvents call. |
| Event patterns | Exact values plus prefix, suffix, exists, equals-ignore-case, numeric and anything-but. |
| Rule validation | PutRule refuses a rule with no trigger, one naming an event bus that does not exist, and one whose pattern cannot be evaluated. |
| Rule deletion | DeleteRule refuses a rule that still has targets, so RemoveTargets comes first. CloudFormation detaches them for you. |
| Delivery | PutEvents evaluates every rule on the bus and delivers matches to Lambda, SQS, SNS, Step Functions, Kinesis, Firehose, ECS RunTask and another event bus. |
| Scheduled rules | rate(...) and AWS’s six-field cron(...) fire on an in-process clock, through the same target dispatcher. |
| Input shaping | Input, InputPath and InputTransformer, at most one per target, over the JSONPath subset AWS uses ($, dotted members, array indexing). |
| Retries and dead-lettering | RetryPolicy.MaximumRetryAttempts, MaximumEventAgeInSeconds measured from the envelope’s time, and a DeadLetterConfig SQS queue. |
| Service-originated events | CloudWatch alarm transitions, S3 object created/deleted, EC2 and ECS state changes, Auto Scaling launch and terminate events, and Step Functions execution status changes publish onto the default bus. |
InputTransformer templates may reference <aws.events.rule-name>,
<aws.events.rule-arn>, <aws.events.event.json> and
<aws.events.event.ingestion-time>. Recent per-target outcomes — delivered,
retried, dead-lettered, dropped — are readable at
GET /_overcast/eventbridge/deliveries, an emulator-only endpoint backed by an
in-memory ring that does not survive a restart.
Differences from AWS
| Area | On AWS | Overcast |
|---|---|---|
| Event patterns | Also has cidr, wildcard and $or | Those three are refused by PutRule |
| Target types | ~20 | Eight; anything else is refused by PutTargets |
| Retry timing | Exponential backoff over up to 24 hours | Immediate, capped at 5 retries |
| Bus-to-bus forwarding | Independent delivery, no hop budget | Nested in-process call, capped at 4 hops |
| Archives, replay, API destinations | Supported | Not implemented |
| Service-originated events | Substantially more | Six publishers |
A target ARN naming an unsupported service comes back in PutTargets’s
FailedEntries with ErrorCode: UnsupportedTargetType, rather than being
stored as a rule that provisions cleanly and never fires.
Gotchas
Warning
cidr, wildcard and $or are refused, not ignored. PutRule and
TestEventPattern answer InvalidEventPatternException naming the match
type, so a rule that could never fire is never stored. Rewrite the clause, or
filter on what the target receives.
PutRule applies the same check to a pattern’s shape: a field whose value is a
bare string rather than an array, and a match type EventBridge does not define,
are both InvalidEventPatternException rather than a rule that provisions and
stays quiet.
Important
Remove a rule’s targets before deleting it. DeleteRule answers
ValidationException while any target is attached, as AWS does. Force does
not help — it is the managed-rule escape, and AWS ignores it for every other
rule. Deleting an AWS::Events::Rule through CloudFormation needs nothing
extra; the stack detaches the targets it attached.
Scheduled rules reach the same targets on an in-process clock, and are as strict about their expressions as AWS is.
Important
A cron(...) expression takes AWS’s six fields, and day-of-week is 1-7
from Sunday. The five-field Unix form is refused, as it is on AWS: every five
minutes is cron(*/5 * * * ? *). L, LW, <day>W, <day>L, <day>#<n>
and the three-letter month and day names all work.
Operations
20 of 31 listed operations are implemented. Per-operation status, notes and AWS API links: EventBridge operations.
Related
- Scheduler — the same target dispatcher, on a clock
- Pipes — point-to-point source → target wiring
- Step Functions — one of the eight target types
- All service pages
- Service names and state overrides
- AWS API reference