README.md

Brucke - Inter-cluster bridge of kafka topics

Brucke is a Inter-cluster bridge of kafka topics powered by Brod

Brucke bridges messages from upstream topic to downstream topic with configurable re-partitionning strategy and message filter/transform plugins

Configuration

A brucke config file is a YAML file.

Config file path should be set in config_file variable of brucke app config, or via BRUCKE_CONFIG_FILE OS env variable.

Cluster names and client names must comply to erlang atom syntax.

kafka_clusters:
  kafka_cluster_1:
    - "localhost:9092"
  kafka_cluster_2:
    - "kafka-1:9092"
    - "kafka-2:9092"
brod_clients:
  - client: brod_client_1
    cluster: kafka_cluster_1
    config: [] # optional
  - client: brod_client_2 # example for SSL connection
    cluster: kafka_cluster_1
    config:
      ssl: true
  - client: brod_client_3 # example for SASL_SSL and custom certificates
    cluster: kafka_cluster_1
    config:
      ssl:
        # start with "priv/" or provide full path
        cacertfile: priv/ssl/ca.crt
        certfile: priv/ssl/client.crt
        keyfile: priv/ssl/client.key
      sasl:
        # or 'plain' or 'scram_sha_256'
        mechanism: scram_sha_512
        username: brucke
        password: secret
routes:
  - upstream_client: brod_client_1
    downstream_client: brod_client_1
    upstream_topics:
      - "topic_1"
    downstream_topic: "topic_2"
    repartitioning_strategy: strict_p2p
    default_begin_offset: earliest # optional
    filter_module: brucke_filter # optional
    filter_init_arg: "" # optional
    upstream_cg_id: example-consumer-group-1 # optional, build from cluster name otherwise

Client Configs

• ssl Either set to true or be specific about the cert/key files to use cacertfile, certfile and keyfile. In case the file paths start with priv/ brucke will look in application priv dir (i.e. code:priv_dir(brucke)).
• sasl Configure SASL auth mechanism, username and password for SASL PLAIN authentication.
• query_api_versions Set to false when connecting to kafka 0.9.x or earlier

See more configs in brod:start_client/4 API doc.

Routing Configs

Upstream Consumer Group ID

upstream_cg_id identifies the consumer group which route workers (maybe distributed across different Erlang nodes) should join in, and commit offsets to. Group IDs don't have to be unique, two or more routes may share the same group ID. However, the same topic may not appear in two routes share the same group ID.

Default Begin Offset

The default_begin_offset route config is to tell upstream consumer from where to start streaming messsages. Supported values are earliest, latest (default) or a kafka offset (integer) value. This config is to tell brucke route worker from which offset it should start streaming messages for the first run. In case of restart, brucke should continue from committed offset.

NOTE: Offsets committed to kafka may expire, in that case, brucke will fallback to this default being offset. NOTE: Currently this option is used for ALL partitions in upstream topic(s).

In case there is a need to discard committed offsets, pick a new group ID.

Offset Commit Policy

The Offset_commit_policy specify how upstream consumer manages the offset per topic-partition. Two values are available: commit_to_kafka_v2 or consumer_managed. when consumer_managed is used, topic-partition offsets will be stored in dets (set). see "PATH to offsets DETS file".

default: commit_to_kafka_v2

Repartitioning strategy

NOTE: For compacted topics, strict_p2p is the only choice.

• key_hash: hash the message key to downstream partition number
• strict_p2p: strictly map the upstream partition number to downstream partition number, worker will refuse to start if upstream and downstream topic has different number of partitions
• random: randomly distribute upstream messages to downstream partitions

Message Transformation

Depending on message format version in kafka broker, possible message formats from kafka are

• Version 0: key-value without timestamp (kafka prior to 0.10)
• Version 1: key-value with timestamp (since kafka 0.10)
• Version 2: key-value with headers and timestamp (since kafka 0.11)

When downstream kafka supports lower version than upstream, unsupported fields are dropped. Otherwise messages are upgraded using default values as below:

• Local host's OS time is used as default timestamp if upstream message message has no create timestamp
• Empty list [] is used as default headers field for downstream message if upstream message has no headers

Customized Message Filtering and or Transformation

Implement brucke_filter behaviour to have messages filtered and or transformed before produced to downstream topic.

If brucke is packed standalone (i.e. not used as a dependency in a parent project), and the beam files for brucke_filter modules are installed elsewhere, configure filter_ebin_dirs app env (sys.config), or set system OS env variables BRUCKE_FILTER_EBIN_PATHS.

Other Routing Options

• compression: no_compression (defulat), gzip or snappy
• max_partitions_per_group_member: default = 12, Number of partitions one group member should work on.
• required_acks: all (default), leader or none

Offsets DETS file

You can config brucke where to start consuming by providing the none empty 'Offsets DETS file' when brucke starts.

It should be set table and the record should be in following spec:

{ {GroupID :: binary() , Topic :: binary(), Partition :: non_neg_integer() }, Offset :: -1 | non_neg_integer() }.

offsets_dets_path specify the PATH to the offsets dets file which is used by 'Offset Commit Policy'. If file does not exists, brucke will create empty one and use it. default: "/tmp/brucke_offsets.DETS"

ratelimit

Ratelimit the number of messages produced to downstream.

ratelimit_interval defines the interval in milliseconds, default: 0 means disabled. ratelimit_threshold defines the threshold, set to 0 to pause.

You can change these two settings in realtime via restapi.

example:

Limit the msg rate of consumer group: group1 of cluster: clusterA to 10 msgs/s:

POST /plugins/ratelimiter/clusterA/group1
{"interval": "100", "threshold", "1"}

Graphite reporting

If the following app config variables are set, brucke will send metrics to a configured graphite endpoint:

• graphite_root_path: a prefix for metrics, e.g "myservice"
• graphite_host: e.g. "localhost"
• graphite_port: e.g. 2003

Alternatively, you can use corresponding OS env variables:

• BRUCKE_GRAPHITE_ROOT_PATH
• BRUCKE_GRAPHITE_HOST
• BRUCKE_GRAPHITE_PORT

RPM packaging

Generate a release and package it into an rpm package:

make rpm

Brucke package installs release and creates corresponding systemd service. Config files are in /etc/brucke, OS env can be set at /etc/sysconfig/brucke, logs are in /var/log/brucke.

Operating via systemctl:

systemctl start brucke
systemctl enable brucke
systemctl status brucke

Script for config validation

Build:

make escript

Usage:

brucke <path/to/config.yml> [filter-module-ebin-dir ...]

Set BRUCKE_FILTER_MODULE_BEAM_DIRS for extra filter module beam lookup. For valid configs the validation command should silently exit with code 0.

Http Endpoint for Healthcheck

Default port is 8080, customize via http_port config option or via BRUCKE_HTTP_PORT OS env variable.

GET /ping

Returns pong if the application is up and running.

GET /healthcheck

Responds with status 200 if everything is OK, and 500 if something is not OK. Also returns healthy and unhealthy routes in response body in JSON format.

Example response:

{
    "discarded": [
        {
            "downstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9192
                    }
                ],
                "topic": "brucke-filter-test-downstream"
            },
            "options": {
                "default_begin_offset": "earliest",
                "filter_init_arg": [],
                "filter_module": "brucke_test_filter",
                "repartitioning_strategy": "strict_p2p"
            },
            "reason": [
                "filter module brucke_test_filter is not found\nreason:embedded\n"
            ],
            "upstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topics": [
                    "brucke-filter-test-upstream"
                ]
            }
        }
    ],
    "healthy": [
        {
            "downstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9192
                    }
                ],
                "topic": "brucke-basic-test-downstream"
            },
            "options": {
                "consumer_config": {
                    "begin_offset": "earliest"
                },
                "filter_init_arg": [],
                "filter_module": "brucke_filter",
                "max_partitions_per_group_member": 12,
                "producer_config": {
                    "compression": "no_compression"
                },
                "repartitioning_strategy": "strict_p2p"
            },
            "upstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topics": "brucke-basic-test-upstream"
            }
        },
        {
            "downstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topic": "brucke-test-topic-2"
            },
            "options": {
                "consumer_config": {
                    "begin_offset": "earliest"
                },
                "filter_init_arg": [],
                "filter_module": "brucke_filter",
                "max_partitions_per_group_member": 12,
                "producer_config": {
                    "compression": "no_compression"
                },
                "repartitioning_strategy": "strict_p2p"
            },
            "upstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topics": "brucke-test-topic-1"
            }
        },
        {
            "downstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topic": "brucke-test-topic-3"
            },
            "options": {
                "consumer_config": {
                    "begin_offset": "latest"
                },
                "filter_init_arg": [],
                "filter_module": "brucke_filter",
                "max_partitions_per_group_member": 12,
                "producer_config": {
                    "compression": "no_compression"
                },
                "repartitioning_strategy": "key_hash"
            },
            "upstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9092
                    }
                ],
                "topics": "brucke-test-topic-2"
            }
        },
        {
            "downstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9192
                    }
                ],
                "topic": "brucke-test-topic-1"
            },
            "options": {
                "consumer_config": {
                    "begin_offset": "latest"
                },
                "filter_init_arg": [],
                "filter_module": "brucke_filter",
                "max_partitions_per_group_member": 12,
                "producer_config": {
                    "compression": "no_compression"
                },
                "repartitioning_strategy": "random"
            },
            "upstream": {
                "endpoints": [
                    {
                        "host": "localhost",
                        "port": 9192
                    }
                ],
                "topics": "brucke-test-topic-3"
            }
        }
    ],
    "status": "failing",
    "unhealthy": []
}