Current state: Accepted
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Today, we can use SCRAM authentication for Kafka Brokers when the cluster uses ZooKeeper (ZK) for the quorum servers. This is possible to bootstrap by first setting up the ZK servers and setting the inter-broker communication password by directly updating them on the ZK before the Kafka Brokers are started. See Configuring SCRAM for details. We wish to implement some similar mechanism for storing the Kafka Broker authentication credentials for SCRAM when the cluster uses KRaft for the quorum servers. We want these credentials to be stored before the Kafka cluster starts for the first time.
We will update the
kafka-storage tool to take SCRAM credentials and store them when we format each node.
kafka-storage tool is used to initialize the storage space for each broker and controller. One of the files created is the
bootstrap.checkpoint which contains a set of
ApiMessageAndVersion records that are needed for the bootstrap process of the cluster. I am proposing we add an interface to the kafka-storage tool so we can add the needed SCRAM credential updates,
UserScramCredentialsRecord which is an
ApiMessageAndVersion record, when the storage is formatted. With this, when the initial start of the cluster happens, each broker will have a copy of the SCRAM server side credential needed so they can communicate with each other.
I propose we add an option
--add-scram to the
kafka-storage tool that will add an
ApiMessageAndVersion records directly into the
__cluster_metadata topic. (See KIP-801 for details on
__cluster_metadata ). The option can be applied multiple times to the format command so that multiple SCRAM records can be added to bootstrap the cluster. Below is the new updates
I propose the SCRAM_CREDENTIAL argument will be a key value pair where the key is one of the SCRAM mechanisms supported, either SCRAM-SHA-256 or SCRAM-SHA-512, and the value is a set of key value pairs of parameters to populate the
UserScramCredentialsRecord. The SCRAM_CREDENTIAL argument is very similar to the argument passed to the
kafka-config tool for configuring SCRAM in a ZK cluster. See Configuring SCRAM for details.
The subarguments for the SCRAM_CREDENTIAL require a "user" key and either a "password" key or a "saltedpassword" key. If using the "saltedpassword" key you must also supply an "iteration" key and a "salt" key. The "iteration" and "salt" key are otherwise optional. However if they are not supplied, "iteration" count will default to 4096 and the "salt" will be randomly generated. The value for "salt" and "saltedpassword" is base64 encoding of binary data.
I propose to also add support for the argument parsing to include taking a file of arguments. This is a standard Argparse4j feature and will make it easier to bootstrap brokers and controllers with multiple SCRAM_CREDENTIALS. I propose to use the '@' character to proceed the filename argument which contains additional arguments. See the Argparse4j fromfileprefix manual entry for details.
Compatibility, Deprecation, and Migration Plan
These changes are additions to the k
afka-storage tool only. There are no backwards compatibility issues with this change.
These changes are to the bootstrap of a cluster and have no impact of existing clusters at all.
The original proposal was for adding raw records to the __cluster_metadata. These records would be describe as a single key value where the key is the name of the ApiMessageAndVersion record and the value a JSON encoding of the fields for that record. An example would be the following for a SCRAM credential record.
This proposal is not very customer friendly as the customer now needs to know what the fields of the underlying
UserScramCredentialsRecordare. It also has the issue that the underlying record format could change in the future requiring the command line to change. It is desired that even if the record format changes, the argument parsing shouldn't be affected.
kafka-configto take a format directory option and use the same arguments for altering SCRAM credentials to add them to the
__cluster_metadatatopic for bootstrap. The issues with this is that it requires multiple commands to format each node in a cluster. It also has the problem of adding a whole new block of code to
kafka-configjust to handle the
bootstrap.checkpointfile and it would need logic to understand if the bootstrap had completed.
- Update k
afka-storageto append records to bootstrap.checkpoint with multiple invocations of the tool. This would allow the use of the same command line arguments from
kafka-configto be used. It was deemed a requirement that a single invocation of
kafka-storageformat all the records for bootstrap.