my question is split to two. I've read Kafka Connect - Delete Connector with configs?. I'd like to completely remove a connector, with offsets and all, so I can recreate it with the same name later. Is this possible? To my understanding, a tombstone message will kill this connector indefinitely.
The second part is - is there a way to have the kafka-connect container automatically delete all connectors he created when bringing it down?
Thanks
There is no such command to completely cleanup connector state. For sink connectors, you can use kafka-consumer-groups to reset it's offsets. For source connectors, it's not as straightforward, as you'll need to manually produce data into the Connect-managed offsets topic.
The config and status topics also persist historical data, but shouldn't prevent you from recreating the connector with the same name/details.
The Connect containers published by Confluent and Debezium always uses Distributed mode. You'll need to override the entrypoint of the container to use standalone mode to not persist the connector metadata in Kafka topics (this won't be fault tolerant, but it'll be fine for testing)
Related
I have Debezium in a container, capturing all changes of PostgeSQL database records.
How to delete all kafka topics which are created already and initiate ad-hoc snapshot from the beginning for all tables configured?
You can use kafka-topics --delete, just like any other topic. The Debezium ones typically match your database schema/table name. You'll also need to find the internal offsets topic created by Kafka Connect framework.
For Docker, though, if you restart Kafka and Zookeeper and they don't have volumes attached, then they'll lose everything, which would be easier for ad-hoc development.
Also, you don't need Zookeeper anymore, as of Kafka 3.3.1
I am running a Debezium connector to PostgreSQL. The snapshot.mode I use is initial, since I don't want to resnapshot just because the connector has been restarted. However, during development I want to restart the process, as the messages expire from Kafka before they have been read.
If I delete and recreate the connector via Kafka Connect REST API, this doesn't do anything, as the information in the offset/status/config topics is preserved. I have to delete and recreate them when restarting the whole connect cluster to trigger another snapshot.
Am I missing a more convenient way of doing this?
You will also need a new name for the connector as well as a new database.server.name name in the connector config, which stores all the offset information. It should almost be like deploying a connector for the first time again.
I have used kafka source connector to get the documents from Couchbase to kafka. These documents are then replicated to Mongo DB.
Couchbase --> Source Connector --> Kafka --> Sink Connector ---> Mongo
If the source connector is down then how to again synch all the documents to Kafka?
Is there any get and touch functionality that can agian event out all the changes made during the down period to the kafka topic?
If you're asking about processing the document changes that occurred while the source connector was down, then you don't need to do anything. Kafka Connect stores the state (offsets) of the source connector and will restore the StreamTask state and continue from where it left off. The Couchbase source connector supports this, as we can see in the code here, which is then used here to initialize the DCP stream with the saved offsets.
If you're asking how to reset the connector and re-stream the entire bucket from the beginning, that's actually not as easy. As far as I know, there is no built-in way in Kafka to reset a connector's offsets - there is a KIP under review related to that: KIP-199 Barring official support, the best way I know of resetting the connector state is either change the config to use a different topic for saving the offsets, which is hacky and leaves the old offsets as a potential problem, or actually edit the saved offsets as described here. I would never advocate doing either of those on a production system, so use your own judgement.
I know how to delete Kafka connector as mentioned here Kafka Connect - How to delete a connector
But I am not sure if it also delete/erase specific connector related configs, offsets and status from *.sorage.topic for that worker?
For e.g:
Lets say I delete a connector having connector-name as"connector-abc-1.0.0" and Kafka connect worker was started with following config.
offset.storage.topic=<topic.name>.internal.offsets
config.storage.topic=<topic.name>.internal.configs
status.storage.topic=<topic.name>.internal.status
Now after DELETE call for that connector, will it erased all records from above internal topics for that specific connector?
So that I can create new connector with "same name" on same worker but different config(different offset.start or connector.class)?
When you delete a connector, the offsets are retained in the offsets topic.
If you recreate the connector with the same name, it will re-use the offsets from the previous execution (even if the connector was deleted in between).
Since Kafka is append only, then only way the messages in those Connect topics would be removed is if it were published with the connector name as the message key, and null as the value.
You could inspect those topics using console consumer to see what data is in them including --property print.key=true, and keep the consumer running when you delete a connector.
You can PUT a new config at /connectors/{name}/config, but any specific offsets that are used are dependent upon the actual connector type (sink / source); for example, there is the internal Kafka __consumer_offsets topic, used by Sink connectors, as well as the offset.storage.topic, optionally used by source connectors.
"same name" on same worker but different config(different offset.start or connector.class)?
I'm not sure changing connector.class would be a good idea with the above in mind since it'd change the connector behavior completely. offset.start isn't a property I'm aware of, so you'll need to see the documentation of that specific connector class to know what it does.
I'm experiencing quite weird behavior working with Confluent JDBC connector. I'm pretty sure that it's not related to Confluent stack, but to Kafka-connect framework itself.
So, I define offset.storage.file.filename property as default /tmp/connect.offsets and run my sink connector. Obviously, I expect connector to persist offsets in the given file (it doesn't exist on file system, but it should be automatically created, right?). Documentation says:
offset.storage.file.filename
The file to store connector offsets in. By storing offsets on disk, a standalone process can be stopped and started on a single node and resume where it previously left off.
But Kafka behaves in completely different manner.
It checks if the given file exists.
It it's not, Kafka just ignores it and persists offsets in Kafka topic.
If I create given file manually, reading fails anyway (EOFException) and offsets are being persisted in topic again.
Is it a bug or, more likely, I don't understand how to work with this configurations? I understand difference between two approaches to persist offsets and file storage is more convenient for my needs.
The offset.storage.file.filename is only used in source connectors, in standalone mode. It is used to place a bookmark on the input data source and remember where it stopped reading it. The created file contains something like the file line number (for a file source) or a table row number (for jdbc source or databases in general).
When running Kafka Connect in distributed mode, this file is replaced by a Kafka topic named by default connect-offsets which should be replicated in order to tolerate failures.
As far as sink connectors are concerned, no matter which plugin or mode (standalone/distributed) is used, they all store where they last stopped reading their input topic in an internal topic named __consumer_offsets like any Kafka consumers. This allows to use traditional tools like kafka-consumer-groups.sh command-line tools to see how the much the sink connector is lagging.
The Confluent Kafka replicator, despite being a source connector, is probably an exception because it reads from a remote Kafka and may use a Kafka consumer, but only one cluster will maintain those original consumer group offsets.
I agree that the documentation is not clear, this setting is required whatever the connector type is (source or sink), but it is only used on by source connectors. The reason behind this design decision is that a single Kafka Connect worker (I mean a single JVM process) can run multiple connectors, potentially both source and sink connectors. Said differently, this setting is worker level setting, not a connector setting.
The property offset.storage.file.filename only applies to workers of source connectors running in standalone mode. If you are seeing Kafka persist offsets in a Kafka topic for a source, you are running in distributed mode. You should be launching your connector with the provided script connect-standalone. There's a description of the different modes here. Instructions on running in the different modes are here.