# Connect Cdc Mongodb > Streams change data capture from MongoDB into Redpanda or Kafka using Redpanda Connect's mongodb_cdc input, built on MongoDB Change Streams over a replica set or sharded cluster. Use when configuring mongodb_cdc, setting up Change Streams, enabling an initial snapshot before live streaming, choosing between update_lookup and pre_and_post_images document modes, or checkpointing with resume tokens in a cache resource. Also covers Redpanda Enterprise destination features like Iceberg Topics, Tiered Storage, and server-side Schema ID Validation, all of which require a Redpanda Enterprise license. - Skill: `redpanda-data/connect-cdc-mongodb-2` (Agent Skill, multi-file: 6 files) - Install (CLI): `npx skillmds@latest add redpanda-data/connect-cdc-mongodb-2` - Raw SKILL.md: https://api.skillmd.com/api/skills/redpanda-data/connect-cdc-mongodb-2/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: redpanda-data (https://skillmd.com/u/redpanda-data) - Updated: 2026-09-22 - Page: https://skillmd.com/skills/redpanda-data/connect-cdc-mongodb-2 --- # Redpanda Connect CDC: MongoDB The `mongodb_cdc` input in Redpanda Connect streams change data capture (CDC) from a MongoDB database into Redpanda or any Kafka-compatible topic. It uses MongoDB Change Streams (requires MongoDB 4.0+ running as a **replica set** or **sharded cluster**), and optionally snapshots all existing documents before switching to live change streaming. This is an **Enterprise feature** — a Redpanda Enterprise license is required. The connector tracks its position in the change stream using a **resume token**, which is stored in a configured cache resource. On restart, it resumes from the last stored token rather than replaying from the beginning. ## Quickstart ### 1. Verify your MongoDB topology Change Streams require a replica set or sharded cluster — they are not available on standalone `mongod` instances. ```bash # Connect via mongosh and check replication status mongosh "mongodb://localhost:27017" rs.status() # must show a replica set configuration # Create a user with read on the target DB # (covers find + listCollections + changeStream action) use admin db.createUser({ user: "cdc_user", pwd: "secret", roles: [ { role: "read", db: "mydb" } ] }) ``` ### 2. Full pipeline YAML (snapshot + stream, two collections) ```yaml # mongodb-cdc-pipeline.yaml cache_resources: - label: mongo_checkpoint memory: compaction_interval: "" # disable compaction/expiry (token persists for process lifetime) input: label: "mongo_cdc" mongodb_cdc: url: "mongodb://cdc_user:secret@localhost:27017/?replicaSet=rs0" database: mydb collections: - orders - customers checkpoint_cache: mongo_checkpoint checkpoint_key: mongodb_cdc_checkpoint # default checkpoint_interval: 5s # default checkpoint_limit: 1000 # default stream_snapshot: true snapshot_parallelism: 2 read_batch_size: 1000 # default read_max_wait: 1s # default document_mode: update_lookup # default json_marshal_mode: canonical # default pipeline: processors: - mapping: | # Route each event to a per-collection topic meta topic = "mongo.cdc." + meta("collection") # Tag the key with the document _id. # In canonical json_marshal_mode (the default) _id is an ExtJSON # object like {"$oid":"..."}, so extract the inner string: meta msg_key = this._id."$oid" | this._id.string() | "" output: redpanda: seed_brokers: ["localhost:9092"] topic: ${! meta("topic") } key: ${! meta("msg_key") } max_in_flight: 256 ``` ### 3. Run the pipeline ```bash rpk connect run mongodb-cdc-pipeline.yaml ``` ### 4. Verify messages arrive ```bash rpk topic consume mongo.cdc.orders --num 5 --brokers localhost:9092 ``` ## Prerequisites - **MongoDB 4.0 or higher** — the connector checks the server version at startup and returns an error for < 4.0. - **Replica set or sharded cluster** — Change Streams are not available on standalone instances. - **User privileges**: at minimum the `read` role on the target database — this covers `find` (snapshot), `listCollections` (schema discovery), and the `changeStream` action (Change Streams). For parallel snapshots via `splitVector` on self-managed clusters, also grant `clusterManager` on `admin`; alternatively set `snapshot_auto_bucket_sharding: true` to avoid that requirement. The `hello`/`buildInfo` startup commands require no special role. - **Redpanda Enterprise license** — the `mongodb_cdc` component is gated by `license.CheckRunningEnterprise`. ## Core Concepts ### Change Streams and Resume Tokens `mongodb_cdc` opens a MongoDB Change Stream over the target database, filtered to the configured collections. MongoDB tracks position via an opaque **resume token** (not an integer offset). The connector stores the latest acknowledged token in the configured cache resource every `checkpoint_interval` (default `5s`), writes one final token on clean shutdown, and — as of Connect 4.106.0 — writes a checkpoint as soon as the initial snapshot completes and is fully acknowledged, so a restart after the snapshot resumes the stream instead of re-snapshotting. On startup, if no cached token is found, the connector: 1. Records the current oplog position. 2. If `stream_snapshot: true`, reads all existing documents (operation = `"read"`). 3. Opens the change stream starting just after the recorded oplog position. If a token is found, the connector resumes directly from that position using `ResumeAfter`. ### Document Modes The `document_mode` field controls what body is emitted for update and delete events: | Mode | Updates | Deletes | |------|---------|---------| | `update_lookup` (default) | Full document after the update (via `UpdateLookup`). Falls back to `documentKey` if the document was deleted before lookup. | Only `_id` populated (documentKey). | | `pre_and_post_images` | Full document before and after (requires MongoDB 6.0+ and `changeStreamPreAndPostImages` enabled on each collection). | Full document before deletion. | | `partial_update` | A structured diff: `{_id, operations: [{path, type, value}]}` where `type` is `set`, `unset`, or `truncatedArray`. Enables `showExpandedEvents` on MongoDB 6.1+. | Only `documentKey`. | ### Message Metadata Every message emitted by `mongodb_cdc` carries: | Metadata key | Value | |---|---| | `operation` | `"read"` (snapshot), `"insert"`, `"update"`, `"replace"`, or `"delete"` | | `collection` | Collection name (e.g., `"orders"`) | | `operation_time` | BSON timestamp in JSON form: `{"$timestamp":{"t":,"i":}}` | | `schema` | Inferred or validator-derived schema in benthos common schema format (immutable; absent when no schema can be determined, e.g., deletes without pre-images) | ### Schema Detection The connector uses a two-tier strategy to populate the `schema` metadata: 1. At startup, it queries each collection's `$jsonSchema` validator. If found, this provides accurate types and required/optional field classification. 2. When no validator exists, schema is inferred from the first document seen per collection. All fields are marked optional. The schema is re-inferred when the top-level field set of a document changes. Type changes within existing fields and nested subdocument structural changes are not auto-detected — restart to force a full schema refresh. **Recommendation**: for schema-registry targets with compatibility modes, configure a `$jsonSchema` validator on each watched collection to stabilize the schema. ### AWS IAM Authentication (MongoDB Atlas) Since Connect 4.106.0, `mongodb_cdc` (and the `mongodb` input, output, processor and cache) can authenticate with the driver-native **`MONGODB-AWS`** mechanism instead of a static username and password, via an `aws` config block: ```yaml input: mongodb_cdc: url: "mongodb+srv://cluster0.abc123.mongodb.net/" database: mydb aws: enabled: true # default false collections: [orders] checkpoint_cache: mongo_checkpoint ``` Rules that matter when choosing this path: - The Atlas database user must be created with the **AWS IAM** authentication type, and connections require TLS. - `aws.enabled: true` is mutually exclusive with `username`/`password` **and** with credentials embedded in `url` — either combination is a startup error. - With no static keys or roles configured, the **ambient AWS credential chain** (environment variables, EC2 instance profile, EKS pod role) is used and expiring credentials are refreshed automatically. Prefer this for long-running pipelines. - Role assumption (`aws.role`, `aws.roles`, or session tokens) is **rejected for the `mongodb` processor and cache**, which establish their client once at creation and cannot refresh expiring session credentials. Use the ambient chain or long-lived access keys there. - With role assumption on `mongodb_cdc`, credentials are re-resolved after the initial snapshot completes, so streaming starts with a full session — but the snapshot itself must finish inside one session, because snapshot progress is not checkpointed. For very large snapshots, prefer the ambient chain. Per-field detail (`region`, `session_duration`, `id`/`secret`/`token`, `role`/`role_external_id`, `roles[]`) is in [Config Reference](references/config-reference.md) and the generated connector reference. ### Snapshot Phase When `stream_snapshot: true` and no resume token is cached, the connector snapshots all documents in each collection before streaming live changes. - **Per-collection concurrency** (always): each collection is snapshotted in its own goroutine, so multiple collections are always snapshotted concurrently regardless of `snapshot_parallelism`. - **Within-collection cursor scan** (`snapshot_parallelism: 1`, the default): each collection is read sequentially with a single cursor. - **Within-collection parallel** (`snapshot_parallelism > 1`): each collection is split into `snapshot_parallelism` `_id`-range buckets read concurrently, using `splitVector` (self-managed, requires `clusterManager` role) or `$bucketAuto` (when `snapshot_auto_bucket_sharding: true`, for Atlas where `splitVector` is disallowed). The `read_batch_size` field controls the MongoDB cursor batch size for both snapshot and streaming phases. ## Checkpoint Cache The `checkpoint_cache` field is **required** — you must provide a named cache resource. This cache stores the resume token as BSON Extended JSON. For development (non-persistent, resets on restart): ```yaml cache_resources: - label: mongo_checkpoint memory: compaction_interval: "" # empty string disables compaction and expiry ``` For production (persistent across restarts), use Redis: ```yaml cache_resources: - label: mongo_checkpoint redis: url: redis://localhost:6379 ``` ## Enabling Pre and Post Images (MongoDB 6+) To use `document_mode: pre_and_post_images`, you must enable this feature on each collection: ```javascript // Enable at collection level db.runCommand({ collMod: "orders", changeStreamPreAndPostImages: { enabled: true } }) ``` This requires **MongoDB 6.0+** — `changeStreamPreAndPostImages` was introduced in 6.0. Use `document_mode: update_lookup` on MongoDB 4.x–5.x. ## Operational Notes ### Oplog Window The resume token references a position in the oplog. If the pipeline falls behind or is stopped for longer than the oplog retention window (default 24 hours on Atlas; configurable with `--oplogMinRetentionHours` on self-managed clusters), MongoDB can no longer resume from the stored token. Size the oplog so the window comfortably exceeds the longest expected lag or downtime under peak write load. ### Unresumable Position Recovery When a stored position can no longer be resumed from (aged out of the oplog, or another non-resumable change-stream condition), the connector no longer just errors out — it recovers rather than retrying a dead position: - **With `stream_snapshot: true`** — it clears the checkpoint and re-runs the snapshot, which loses nothing. A breaker bounds this: after 3 consecutive recoveries with no change-stream advance in between (usually a snapshot that takes longer than the oplog window), it keeps the checkpoint and fails on every reconnect with an actionable error instead of re-snapshotting forever. Fix the underlying cause — grow the oplog, speed the snapshot up — then restart the pipeline (or delete the checkpoint cache entry) to resume recovery. - **With `stream_snapshot: false`** — there is no snapshot to re-run, so recovery would mean skipping the changes between the lost position and now. The connector refuses to do that silently: `on_unresumable_position` (default `fail`) preserves the checkpoint and errors on every reconnect; skipping the gap must be opted into with `on_unresumable_position: reset`. `checkpoint_write_timeout` (default `10s`, advanced) bounds the two checkpoint writes that run outside the read loop — storing the position a completed snapshot reached, and clearing an unresumable one — so a slow cache cannot extend shutdown indefinitely. Raise it for slow remote caches (`redis`, `dynamodb`), where losing the post-snapshot write costs a full re-snapshot on the next start. ### Restart Behavior On restart with a valid cached token, the connector immediately opens the change stream at the stored position — no snapshot is performed regardless of the `stream_snapshot` setting. The snapshot only runs when no checkpoint exists; because the completed snapshot's position is now checkpointed once fully acknowledged, a restart after a finished snapshot resumes the stream rather than snapshotting again. ### Scaling All configured collections are consumed through a **single database-level change stream** — the collection list is a server-side filter on that one stream, not a set of independent streams. A change stream is one totally-ordered cursor over the replica set's oplog, so throughput does not grow with more collections, and the input does not use CPU beyond roughly two cores. This is a property of MongoDB change streams, not of the connector. To scale past that ceiling, shard the cluster: a change stream against a sharded cluster merges parallel per-shard cursors server-side. ### Atlas / Restricted Environments On MongoDB Atlas, the `splitVector` command is not available. Set `snapshot_auto_bucket_sharding: true` to use `$bucketAuto` aggregation for parallel snapshots instead. ## Enterprise Features Around the CDC Topic The `mongodb_cdc` input is itself an **Enterprise** connector, and the topics it feeds pair with other Redpanda enterprise differentiators (all require a valid Enterprise license — see [Enterprise Integration](references/enterprise-integration.md) for nested keys and examples): - **Iceberg Topics** — make the CDC output topic a queryable Iceberg table. Set cluster `iceberg_enabled=true`, then topic `redpanda.iceberg.mode` (`key_value` for raw CDC JSON, or `value_schema_id_prefix`/`value_schema_latest` for schema-serialized events), plus `redpanda.iceberg.delete`, `redpanda.iceberg.invalid.record.action` (`drop`/`dlq_table`), `redpanda.iceberg.partition.spec`, `redpanda.iceberg.target.lag.ms`. - **Server-side Schema ID Validation** — cluster `enable_schema_id_validation` (`none`/`redpanda`/`compat`); topic `redpanda.value.schema.id.validation` + `redpanda.value.subject.name.strategy` (and key equivalents). - **Tiered Storage** — long-term CDC retention: topic `redpanda.remote.write` + `redpanda.remote.read`, with `retention.local.target.ms`/`.bytes` bounding the local footprint. - **Sink security** — TLS (`tls.client_certs[]`, `tls.root_cas_file`) and SASL (`sasl[].mechanism`: `SCRAM-SHA-512`/`PLAIN`/`OAUTHBEARER`); OAUTHBEARER/OIDC and Kerberos broker auth are Enterprise. - **RBAC, Connect secrets management, FIPS, allow/deny component lists** — harden the pipeline and resolve the MongoDB/SASL passwords from a remote secret store. ## Reference Directory - [Config Reference](references/config-reference.md): Every `mongodb_cdc` input field with type, default, and description grounded in source. - [Setup MongoDB](references/setup-mongodb.md): Replica-set/sharded-cluster requirement, user privileges, Atlas specifics, and oplog configuration. - [Pipeline and Output](references/pipeline-and-output.md): Full pipeline YAML examples, message/metadata shape, per-collection routing, cache options, and restart/resume semantics. - [Enterprise Integration](references/enterprise-integration.md): Enterprise features around the CDC topic and their nested config keys — Iceberg Topics (`redpanda.iceberg.*`), Server-side Schema ID Validation (`enable_schema_id_validation`, `redpanda.{key,value}.schema.id.validation`), Tiered Storage (`redpanda.remote.*`, `retention.local.target.*`), sink TLS + SASL (SCRAM/OAUTHBEARER/Kerberos), RBAC, Connect secrets management, FIPS, and allow/deny lists. Notes which require an Enterprise license.