# Twins

Service twins is used for CRUD and update of digital twins. Twin is a semantic
representation of a real world entity, be it device, application or something
else. It holds the sequence of attribute based definitions of a real world thing
and refers to the time series of definition based states that hold the
historical data about the represented real world thing.

## 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_NAME           | 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_THING_ID          | ID of thing representing twins service & mqtt user                   |                       |
| MF_TWINS_THING_KEY         | Key of thing representing twins service & mqtt pass                  |                       |
| MF_TWINS_CHANNEL_ID        | Mqtt notifications topic                                             |                       |
| MF_NATS_URL                | Mainflux NATS broker URL                                             | nats://127.0.0.1:4222 |
| MF_AUTHN_GRPC_PORT         | Authn service gRPC port                                              | 8181                  |
| MF_AUTHN_TIMEOUT           | Authn gRPC request timeout in seconds                                | 1                     |
| MF_AUTHN_URL               | Authn service URL                                                    | localhost:8181        |

## 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:

```yaml
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_NAME: [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_THING_ID: [ID of thing representing twins service]
      MF_TWINS_THING_KEY: [Key of thing representing twins service]
      MF_TWINS_CHANNEL_ID: [Mqtt notifications topic]
      MF_NATS_URL: [Mainflux NATS broker URL]
      MF_AUTHN_GRPC_PORT: [Authn service gRPC port]
      MF_AUTHN_TIMEOUT: [Authn gRPC request timeout in seconds]
      MF_AUTHN_URL: [Authn service URL]
```

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

```bash
# 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_NAME: [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_THING_ID: [ID of thing representing twins service] MF_TWINS_THING_KEY: [Key of thing representing twins service] MF_TWINS_CHANNEL_ID: [Mqtt notifications topic] MF_NATS_URL: [Mainflux NATS broker URL] MF_AUTHN_GRPC_PORT: [Authn service gRPC port] MF_AUTHN_TIMEOUT: [Authn gRPC request timeout in seconds] MF_AUTHN_URL: [Authn service URL] $GOBIN/mainflux-twins
```

## Usage

For more information about service capabilities and its usage, please check out
the [API documentation](swagger.yaml).

[doc]: http://mainflux.readthedocs.io