Bedrock Agent Runtime

InvokeAgent, Retrieve, RetrieveAndGenerate, flow execution, sessions, memory — Bedrock Agent data plane with real eventstream framing.

fakecloud implements the Bedrock Agent Runtime data plane: agent invocation, knowledge-base retrieval, retrieve-and-generate, flow execution, session and memory management, prompt optimization, and reranking. Streaming responses use real AWS eventstream framing (prelude, headers, payload, CRCs) so any AWS SDK can parse the response without special-casing the emulator.

For the control plane (CreateAgent, knowledge bases, action groups, flows), see Bedrock Agent.

Operations

Agent invocation

  • InvokeAgent — POST /agents/{agentId}/agentAliases/{agentAliasId}/sessions/{sessionId}/text. Returns application/vnd.amazon.eventstream with real framed events: chunk (assistant text), trace (orchestration / pre-processing / post-processing / knowledge-base lookup / action-group invocation), and optional returnControl (when an action group is declared RETURN_CONTROL).
  • InvokeInlineAgent — pass the agent definition in the request, no agentId needed. Same eventstream contract as InvokeAgent.
  • InvokeFlow — execute a prepared flow. Eventstream of flowOutputEvent, flowTraceEvent, flowCompletionEvent.

Retrieval

  • Retrieve — query a knowledge base, returns retrievalResults[] with content, location, score, metadata.
  • RetrieveAndGenerate — non-streaming RAG. Combines retrieval with a model call and returns output.text, citations[], sessionId, guardrailAction.
  • RetrieveAndGenerateStream — streaming variant. Eventstream of output, citation, and guardrail events.
  • Rerank — re-score a list of sources against a query using a reranker model.

Flow execution (long-running flows)

  • StartFlowExecution, StopFlowExecution
  • GetFlowExecution, ListFlowExecutions, ListFlowExecutionEvents
  • GetExecutionFlowSnapshot

Sessions

  • CreateSession, GetSession, UpdateSession, ListSessions, EndSession, DeleteSession
  • CreateInvocation, ListInvocations
  • PutInvocationStep, GetInvocationStep, ListInvocationSteps

Memory

  • GetAgentMemory — return persisted memory (SESSION_SUMMARY) for an agent
  • DeleteAgentMemory

Misc

  • OptimizePrompt — rewrite a prompt for a target model (eventstream)
  • GenerateQuery — generate a structured query for a knowledge base
  • TagResource, UntagResource, ListTagsForResource

Protocol

REST + JSON for non-streaming ops, REST + application/vnd.amazon.eventstream for InvokeAgent / InvokeFlow / InvokeInlineAgent / RetrieveAndGenerateStream / OptimizePrompt.

Eventstream framing

The eventstream encoder produces AWS-compliant binary frames: 12-byte prelude (total length, headers length, prelude CRC32), header block, payload, and trailing message CRC32. Both :event-type and :content-type headers are emitted per frame so SDKs decode the same shapes they decode against real AWS. This means streaming tests work end-to-end through boto3, aws-sdk-js, aws-sdk-go-v2, and the Java/Kotlin SDKs without mocking the body decoder.

State model

  • InvokeAgent canned responses default to a single-chunk echo of the input, with traces for preProcessingTrace, orchestrationTrace, and (when knowledge bases are attached) knowledgeBaseLookupTrace. The first call on a fresh session returns a sessionId matching the path segment.
  • RetrieveAndGenerate canned responses include a citation back to the first knowledge-base document returned by Retrieve, so RAG round-trip tests assert on citation plumbing.
  • Sessions persist sessionMetadata and encryptionKeyArn. Invocation steps persist the verbatim payload.

Limitations

  • No real model inference. Responses come from the same configurable-response / echo path documented under Bedrock.
  • No real vector retrieval. Retrieve and RetrieveAndGenerate return synthetic results derived from the data sources attached to the knowledge base.
  • Action group Lambda executors are not invoked; the runtime emits a RETURN_CONTROL event so test code asserting on the agent's action-group contract receives the same shape it would receive from a real RETURN_CONTROL action group.

Source