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Twins

Service twins is used for CRUD and update of digital twins. Twin is a semantic representation of a real world data system consisting of data producers and consumers. It stores the sequence of attribute based definitions of a system and refers to a time series of definition based states that store the system historical data.

Configuration

The service is configured using the environment variables presented in the following table. Note that any unset variables will be replaced with their default values.

Variable	Description	Default
MF_TWINS_LOG_LEVEL	Log level for twin service (debug, info, warn, error)	error
MF_TWINS_HTTP_PORT	Twins service HTTP port	9021
MF_TWINS_SERVER_CERT	Path to server certificate in PEM format
MF_TWINS_SERVER_KEY	Path to server key in PEM format
MF_JAEGER_URL	Jaeger server URL
MF_TWINS_DB	Database name	mainflux
MF_TWINS_DB_HOST	Database host address	localhost
MF_TWINS_DB_PORT	Database host port	27017
MF_TWINS_SINGLE_USER_EMAIL	User email for single user mode (no gRPC communication with users)
MF_TWINS_SINGLE_USER_TOKEN	User token for single user mode that should be passed in auth header
MF_TWINS_CLIENT_TLS	Flag that indicates if TLS should be turned on	false
MF_TWINS_CA_CERTS	Path to trusted CAs in PEM format
MF_TWINS_MQTT_URL	Mqtt broker URL for twin CRUD and states update notifications	tcp://localhost:1883
MF_TWINS_CHANNEL_ID	Mqtt notifications topic
MF_NATS_URL	Mainflux NATS broker URL	nats://localhost:4222
MF_AUTHN_GRPC_URL	AuthN service gRPC URL	localhost:8181
MF_AUTHN_GRPC_TIMEOUT	AuthN service gRPC request timeout in seconds	1

Deployment

The service itself is distributed as Docker container. The following snippet provides a compose file template that can be used to deploy the service container locally:

version: "3"
services:
  twins:
    image: mainflux/twins:[version]
    container_name: [instance name]
    ports:
      - [host machine port]:[configured HTTP port]
    environment:
      MF_TWINS_LOG_LEVEL: [Twins log level]
      MF_TWINS_HTTP_PORT: [Service HTTP port]
      MF_TWINS_SERVER_CERT: [String path to server cert in pem format]
      MF_TWINS_SERVER_KEY: [String path to server key in pem format]
      MF_JAEGER_URL: [Jaeger server URL]
      MF_TWINS_DB: [Database name]
      MF_TWINS_DB_HOST: [Database host address]
      MF_TWINS_DB_PORT: [Database host port]
      MF_TWINS_SINGLE_USER_EMAIL: [User email for single user mode]
      MF_TWINS_SINGLE_USER_TOKEN: [User token for single user mode]
      MF_TWINS_CLIENT_TLS: [Flag that indicates if TLS should be turned on]
      MF_TWINS_CA_CERTS: [Path to trusted CAs in PEM format]
      MF_TWINS_MQTT_URL: [Mqtt broker URL for twin CRUD and states]
      MF_TWINS_CHANNEL_ID: [Mqtt notifications topic]
      MF_NATS_URL: [Mainflux NATS broker URL]
      MF_AUTHN_GRPC_URL: [AuthN service gRPC URL]
      MF_AUTHN_GRPC_TIMEOUT: [AuthN service gRPC request timeout in seconds]

To start the service outside of the container, execute the following shell script:

# download the latest version of the service
go get github.com/mainflux/mainflux

cd $GOPATH/src/github.com/mainflux/mainflux

# compile the twins
make twins

# copy binary to bin
make install

# set the environment variables and run the service
MF_TWINS_LOG_LEVEL: [Twins log level] \
MF_TWINS_HTTP_PORT: [Service HTTP port] \
MF_TWINS_SERVER_CERT: [String path to server cert in pem format] \
MF_TWINS_SERVER_KEY: [String path to server key in pem format] \
MF_JAEGER_URL: [Jaeger server URL] MF_TWINS_DB: [Database name] \
MF_TWINS_DB_HOST: [Database host address] \
MF_TWINS_DB_PORT: [Database host port] \
MF_TWINS_SINGLE_USER_EMAIL: [User email for single user mode] \
MF_TWINS_SINGLE_USER_TOKEN: [User token for single user mode] \
MF_TWINS_CLIENT_TLS: [Flag that indicates if TLS should be turned on] \
MF_TWINS_CA_CERTS: [Path to trusted CAs in PEM format] \
MF_TWINS_MQTT_URL: [Mqtt broker URL for twin CRUD and states] \
MF_TWINS_CHANNEL_ID: [Mqtt notifications topic] \
MF_NATS_URL: [Mainflux NATS broker URL] \
MF_AUTHN_GRPC_URL: [AuthN service gRPC URL] \
MF_AUTHN_GRPC_TIMEOUT: [AuthN service gRPC request timeout in seconds] \
$GOBIN/mainflux-twins

Usage

Starting twins service

The twins service publishes notifications on a NATS subject of the format channels.<MF_TWINS_CHANNEL_ID>.messages.<twinID>.<crudOp>, where crudOp stands for the crud operation done on twin - create, update, delete or retrieve - or state - save state. In order to use twin service notifications, one must inform it - via environment variables - about the Mainflux channel used for notification publishing. You must use an already existing channel, since you cannot know in advance or set the channel id (Mainflux does it automatically).

To set the environment variable, please go to .env file and set the following variable:

MF_TWINS_CHANNEL_ID=

with the corresponding values of the desired channel. If you are running mainflux natively, than do the same thing in the corresponding console environment.

For more information about service capabilities and its usage, please check out the API documentation.

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