strands_session_dynamodb 0.2.0

Amazon DynamoDB session manager (storage backend) for Strands Agents — persists sessions, agent state, and messages

strands-session-dynamodb

Amazon DynamoDB session manager (storage backend) for Strands Agents. Persists an agent's sessions, agent state, conversation-manager state, and messages to a single DynamoDB table so conversations resume across runs.

It implements Strands' SessionRepository and mixes in RepositorySessionManager — exactly like the built-in S3SessionManager — so all the session lifecycle logic (message indexing, restore, removed_message_count offsetting, tool-use repair, change detection) is reused unchanged. This package only supplies the DynamoDB storage.

Storage only, by design. In Strands, message pruning is the job of a ConversationManager (SlidingWindow, Summarizing), which is deliberately decoupled from storage. This package does not prune — pruning at the storage layer would corrupt Strands' message-index/offset restore logic. Use a conversation_manager for that.

Why DynamoDB instead of S3

Strands ships an S3SessionManager out of the box, so why DynamoDB? Because agent sessions are a request-bound, small-item workload — the exact shape where DynamoDB wins on both cost and latency.

Strands writes one item per message plus an agent record re-synced each turn — lots of tiny (sub-KB) reads and writes. The bill is dominated by request count, not bytes stored, and that's where the two services price very differently:

	S3 Standard	DynamoDB on-demand
Write	~$5.00 / million PUT (any size)	~$1.25 / million WRU (per 1 KB)
Read	~$0.40 / million GET (per object)	~$0.25 / million RRU (per 4 KB)
Free tier	none	25 WCU + 25 RCU + 25 GB, perpetual
Latency	tens of ms	single-digit ms

Two structural advantages for small items:

• Writes: S3 charges per request regardless of size — a 200-byte message costs the same PUT as a 4 MB one. DynamoDB bills per KB, so tiny messages hit the cheapest unit and the per-unit price is ~4× lower.
• Reads: list_messages is one Query in DynamoDB, and one RRU covers 4 KB — so several small messages per RRU. In S3 it's one GET per message object. Batching crushes the per-item read cost.

For a workload of ~1M small message-writes/month with periodic restores, this is roughly a 3–4× lower bill on DynamoDB — and often free under DynamoDB's perpetual free tier, which S3 has no equivalent of. Add native TTL for automatic session expiry and single-digit-ms access, and DynamoDB is the better default for hot session/agent-state storage.

When S3 still wins: very large message payloads (big tool results, images) that approach or exceed DynamoDB's 400 KB item limit, or cold/archival sessions rarely read (S3 storage is ~10× cheaper per GB). A robust production setup is DynamoDB for the session/message records + S3 overflow only for oversized blobs.

Installation

pip install strands-session-dynamodb
# or, via the family's extra:
pip install "strands-agents-session[dynamodb]"

Requires Python 3.10+.

Quick start

from strands import Agent
from strands_session_dynamodb import DynamoDBSessionManager

session_manager = DynamoDBSessionManager(
    session_id="user-123",
    table_name="strands-sessions",
    region_name="us-east-1",
)

agent = Agent(session_manager=session_manager)

agent("Hi, I'm Kamal")
agent("What's my name?")   # remembers within the session

Next run, same session_id → the agent restores its full history and state from DynamoDB. The table is created automatically (on-demand billing) if it does not exist.

API

DynamoDBSessionManager(session_id, table_name, *, region_name=None, boto_session=None, boto_client_config=None, endpoint_url=None, ttl_seconds=None)

Parameter	Description
session_id	Session identifier
table_name	DynamoDB table (auto-created if absent)
region_name	AWS region
boto_session	Optional pre-built boto3.Session
boto_client_config	Optional botocore client config
endpoint_url	Custom endpoint (e.g. DynamoDB Local / LocalStack)
ttl_seconds	If set, writes a ttl epoch attribute and enables table TTL for automatic session expiry

AWS setup

Standard AWS credential resolution (env vars, ~/.aws/credentials, profile, or IAM role). The credentials need permission to create the table (if absent) and read/write items.

Data model

Single table, both keys strings:

Item	PK	SK
Session	SESSION#<session_id>	META
Agent	SESSION#<session_id>	AGENT#<agent_id>
Message	SESSION#<session_id>#AGENT#<agent_id>	MSG#<zero-padded id>

Messages live in a per-agent partition with a zero-padded, lexically ordered sort key, so list_messages(offset, limit) is a native range Query — matching the removed_message_count offset semantics Strands relies on. Payloads are stored as a JSON string.

Item-size note: DynamoDB items are capped at 400 KB. A single message with a very large payload (e.g. big tool results / images) could exceed that; S3 has no such limit. For such workloads, keep large blobs in S3 and reference them.

License

MIT