Kafka Bridge

The technical documentation of the kafka-bridge microservice, which acts as a communication bridge between two Kafka brokers.

4 minute read

Kafka-bridge is a microservice that connects two Kafka brokers and forwards messages between them. It is used to connect the local broker of the edge computer with the remote broker on the server.

How it works

This microservice has two ways of operation:

High Integrity: This mode is used for topics that are critical for the user. It is garanteed that no messages are lost. This is achieved by committing the message only after it has been successfully inserted into the database. Ususally all the topics are forwarded in this mode, except for processValue, processValueString and raw messages.
High Throughput: This mode is used for topics that are not critical for the user. They are forwarded as fast as possible, but it is possible that messages are lost, for example if the database struggles to keep up. Usually only the processValue, processValueString and raw messages are forwarded in this mode.

Kubernetes resources

Deployment: united-manufacturing-hub-kafkabridge
Secret:
- Local broker: united-manufacturing-hub-kafkabridge-secrets-local
- Remote broker: united-manufacturing-hub-kafkabridge-secrets-remote

Configuration

You can configure the kafka-bridge microservice by setting the following values in the _000_commonConfig.kafkaBridge section of the Helm chart values file.

  kafkaBridge:
    enabled: true
    remotebootstrapServer: ""
    topicmap:
      - bidirectional: false
        name: HighIntegrity
        send_direction: to_remote
        topic: ^ia\..+\..+\..+\.((addMaintenanceActivity)|(addOrder)|(addParentToChild)|(addProduct)|(addShift)|(count)|(deleteShiftByAssetIdAndBeginTimestamp)|(deleteShiftById)|(endOrder)|(modifyProducedPieces)|(modifyState)|(productTag)|(productTagString)|(recommendation)|(scrapCount)|(startOrder)|(state)|(uniqueProduct)|(scrapUniqueProduct))$
      - bidirectional: false
        name: HighThroughput
        send_direction: to_remote
        topic: ^ia\..+\..+\..+\.(processValue).*$

Topic Map schema

The topic map is a list of objects, each object represents a topic (or a set of topics) that should be forwarded. The following JSON schema describes the structure of the topic map:

{
    "$schema": "http://json-schema.org/draft-07/schema",
    "type": "array",
    "title": "Kafka Topic Map",
    "description": "This schema validates valid Kafka topic maps.",
    "default": [],
    "additionalItems": true,
    "items": {
        "$id": "#/items",
        "anyOf": [
            {
                "$id": "#/items/anyOf/0",
                "type": "object",
                "title": "Unidirectional Kafka Topic Map with send direction",
                "description": "This schema validates entries, that are unidirectional and have a send direction.",
                "default": {},
                "examples": [
                    {
                        "name": "HighIntegrity",
                        "topic": "^ia\\..+\\..+\\..+\\.(?!processValue).+$",
                        "bidirectional": false,
                        "send_direction": "to_remote"
                    }
                ],
                "required": [
                    "name",
                    "topic",
                    "bidirectional",
                    "send_direction"
                ],
                "properties": {
                    "name": {
                        "$id": "#/items/anyOf/0/properties/name",
                        "type": "string",
                        "title": "Entry Name",
                        "description": "Name of the map entry, only used for logging & tracing.",
                        "default": "",
                        "examples": [
                            "HighIntegrity"
                        ]
                    },
                    "topic": {
                        "$id": "#/items/anyOf/0/properties/topic",
                        "type": "string",
                        "title": "The topic to listen on",
                        "description": "The topic to listen on, this can be a regular expression.",
                        "default": "",
                        "examples": [
                            "^ia\\..+\\..+\\..+\\.(?!processValue).+$"
                        ]
                    },
                    "bidirectional": {
                        "$id": "#/items/anyOf/0/properties/bidirectional",
                        "type": "boolean",
                        "title": "Is the transfer bidirectional?",
                        "description": "When set to true, the bridge will consume and produce from both brokers",
                        "default": false,
                        "examples": [
                            false
                        ]
                    },
                    "send_direction": {
                        "$id": "#/items/anyOf/0/properties/send_direction",
                        "type": "string",
                        "title": "Send direction",
                        "description": "Can be either 'to_remote' or 'to_local'",
                        "default": "",
                        "examples": [
                            "to_remote",
                            "to_local"
                        ]
                    }
                },
                "additionalProperties": true
            },
            {
                "$id": "#/items/anyOf/1",
                "type": "object",
                "title": "Bi-directional Kafka Topic Map with send direction",
                "description": "This schema validates entries, that are bi-directional.",
                "default": {},
                "examples": [
                    {
                        "name": "HighIntegrity",
                        "topic": "^ia\\..+\\..+\\..+\\.(?!processValue).+$",
                        "bidirectional": true
                    }
                ],
                "required": [
                    "name",
                    "topic",
                    "bidirectional"
                ],
                "properties": {
                    "name": {
                        "$id": "#/items/anyOf/1/properties/name",
                        "type": "string",
                        "title": "Entry Name",
                        "description": "Name of the map entry, only used for logging & tracing.",
                        "default": "",
                        "examples": [
                            "HighIntegrity"
                        ]
                    },
                    "topic": {
                        "$id": "#/items/anyOf/1/properties/topic",
                        "type": "string",
                        "title": "The topic to listen on",
                        "description": "The topic to listen on, this can be a regular expression.",
                        "default": "",
                        "examples": [
                            "^ia\\..+\\..+\\..+\\.(?!processValue).+$"
                        ]
                    },
                    "bidirectional": {
                        "$id": "#/items/anyOf/1/properties/bidirectional",
                        "type": "boolean",
                        "title": "Is the transfer bidirectional?",
                        "description": "When set to true, the bridge will consume and produce from both brokers",
                        "default": false,
                        "examples": [
                            true
                        ]
                    }
                },
                "additionalProperties": true
            }
        ]
    },
    "examples": [
   {
      "name":"HighIntegrity",
      "topic":"^ia\\..+\\..+\\..+\\.(?!processValue).+$",
      "bidirectional":true
   },
   {
      "name":"HighThroughput",
      "topic":"^ia\\..+\\..+\\..+\\.(processValue).*$",
      "bidirectional":false,
      "send_direction":"to_remote"
   }
]
}

Environment variables

Environment variables
Variable name	Description	Type	Allowed values	Default
`DEBUG_ENABLE_FGTRACE`	Enables the use of the fgtrace library, do not enable in production	string	`true`, `false`	`false`
`KAFKA_GROUP_ID_SUFFIX`	Identifier appended to the kafka group ID, usually a serial number	string	Any	defalut
`KAFKA_SSL_KEY_PASSWORD_LOCAL`	Password for the SSL key pf the local broker	string	Any	""
`KAFKA_SSL_KEY_PASSWORD_REMOTE`	Password for the SSL key of the remote broker	string	Any	""
`KAFKA_TOPIC_MAP`	A json map of the kafka topics should be forwarded	JSON	See below	{}
`KAKFA_USE_SSL`	Enables the use of SSL for the kafka connection	string	`true`, `false`	`false`
`LOCAL_KAFKA_BOOTSTRAP_SERVER`	URL of the local kafka broker, port is required	string	Any valid URL	united-manufacturing-hub-kafka:9092
`LOGGING_LEVEL`	Defines which logging level is used, mostly relevant for developers.	string	PRODUCTION, DEVELOPMENT	PRODUCTION
`MICROSERVICE_NAME`	Name of the microservice (used for tracing)	string	Any	united-manufacturing-hub-kafka-bridge
`REMOTE_KAFKA_BOOTSTRAP_SERVER`	URL of the remote kafka broker	string	Any valid URL	""
`SERIAL_NUMBER`	Serial number of the cluster (used for tracing)	string	Any	defalut

Last modified April 17, 2023: build: version 0.9.13 (6cb0a01)