The Persistence Plugin Architecture is intended to address decoupling persistence implementations from the EdgeX Foundry code base. The core-data, core-metadata, export-client, support-logging and support-notifications services all currently rely on database persistence. Today (Delhi release), persistence implementations are part and parcel of the EdgeX Golang Services repo. As a result, adding a new persistence implementation or updating an existing implementation requires all team members to have knowledge of every supported persistence platform as well as access to an installation of each in order to fully test any changes. New capabilities must be added to every persistence implementation before they can be called complete. This is not scalable. For a future (Edinburgh) release, the goal is to move persistence implementations into their own repos so they can be maintained independently of the EdgeX code base.
The proposed architectural solution utilizes Go Plugins.
Within each service, a configuration value will drive which persistence plugin to load, similar to what we do now. This value can be the same across all services or even different for every service should a customer feel that one or another platform is best suited to the role the service plays in their environment. Each service defines an interface for the necessary database operations (core-data, core-metadata) and then a vendor's plugin must conform to and support that interface.
The design has two major roles: the provider and the platform.
The provider maintains their plugin in their own repository along with the build scripts to create the plugin, the EdgeX build fragments needed by the platform build, and the EdgeX Compose file fragments needed to create the EdgeX Compose file.
The provider repo follows the Go standard project layout. In addition, providers can distribute prebuilt versions of their plugin. The `.so` lives in `pkg/NAME.so.VERSION` where NAME is the plugin name and VERSION follows Semantic Versioning 2.0.
[Databases] [Databases.Primary] Host = 'localhost' Name = 'coredata' Username = 'tiger' Password = 'scott' Port = 1234 Timeout = 5000 Type = 'some-plugin.so.1.0.1' URL = 'https://github.com/some-provider/edgex-plugin/blob/master/pkg' |
some-provider: image: some-provider:alpine ports: - "1234:1234" container_name: edgex-some-provider hostname: edgex-some-provider networks: - edgex-network volumes: - data:/data depends_on: - volume |
The basis of the requirements came out of looking at how others have solved this challenge. Also, note Vladimir Vivien's helpful article on "Writing Modular Go Programs with Plugins".
Azure IoT Edge is organized around independently configured modules (aka containers) that are grouped to form a solution. Each module is described independently and then combined into a solution with a deployment manifest. For example, the RedisEdge module is described using the following module.json
.
{ "$schema-version": "0.0.1", "description": "RedisEdge", "image": { "repository": "$CONTAINER_REGISTRY_ADDRESS/redis-edge", "tag": { "version": "1.0.0", "platforms": { "amd64": "./Dockerfile.amd64", "arm32v7": "./Dockerfile.arm32v7", "arm64v8": "./Dockerfile.arm64v8" } }, "buildOptions": [] }, "language": "javascript" } |
To build a solution with this module, a deployment manifest is constructed using scripts that parse a deployment template which enumerates the modules along with their configuration. Note the use environment variables; these are populated from a .env
file that is not part of the source repository.
{ "modulesContent": { "$edgeAgent": { "properties.desired": { "schemaVersion": "1.0", "runtime": { "type": "docker", "settings": { "minDockerVersion": "v1.25", "loggingOptions": "", "registryCredentials": { "myiotregistery": { "username": "$CONTAINER_REGISTRY_USERNAME", "password": "$CONTAINER_REGISTRY_PASSWORD", "address": "$CONTAINER_REGISTRY_ADDRESS" } } } }, "systemModules": { "edgeAgent": { "type": "docker", "settings": { "image": "mcr.microsoft.com/azureiotedge-agent:1.0", "createOptions": "" } }, "edgeHub": { "type": "docker", "status": "running", "restartPolicy": "always", "settings": { "image": "mcr.microsoft.com/azureiotedge-hub:1.0", "createOptions": "{\"HostConfig\":{\"PortBindings\":{\"5671/tcp\":[{\"HostPort\":\"5671\"}], \"8883/tcp\":[{\"HostPort\":\"8883\"}],\"443/tcp\":[{\"HostPort\":\"443\"}]}}}" } } }, "modules": { "RedisEdge": { "version": "1.0", "type": "docker", "status": "running", "restartPolicy": "always", "settings": { "image": "${MODULES.RedisEdge.amd64}", "createOptions": "{\"HostConfig\": { \"PortBindings\": { \"6379/tcp\": [ { \"HostPort\": \"6379\" } ] } } }" } } } } }, "$edgeHub": { "properties.desired": { "schemaVersion": "1.0", "routes": {}, "storeAndForwardConfiguration": { "timeToLiveSecs": 7200 } } } } } |
Which results in the following deployment manifest
{ "modulesContent": { "$edgeAgent": { "properties.desired": { "schemaVersion": "1.0", "runtime": { "type": "docker", "settings": { "minDockerVersion": "v1.25", "loggingOptions": "" } }, "systemModules": { "edgeAgent": { "type": "docker", "settings": { "image": "mcr.microsoft.com/azureiotedge-agent:1.0", "createOptions": "" } }, "edgeHub": { "type": "docker", "status": "running", "restartPolicy": "always", "settings": { "image": "mcr.microsoft.com/azureiotedge-hub:1.0", "createOptions": "{\"HostConfig\":{\"PortBindings\":{\"5671/tcp\":[{\"HostPort\":\"5671\"}], \"8883/tcp\":[{\"HostPort\":\"8883\"}],\"443/tcp\":[{\"HostPort\":\"443\"}]}}}" } } }, "modules": { "RedisEdge": { "version": "1.0", "type": "docker", "status": "running", "restartPolicy": "always", "settings": { "image": "andresandboxregistry.azurecr.io/redis-edge:1.0.0-amd64", "createOptions": "{\"HostConfig\": { \"PortBindings\": { \"6379/tcp\": [ { \"HostPort\": \"6379\" } ] } } }" } } } } }, "$edgeHub": { "properties.desired": { "schemaVersion": "1.0", "routes": {}, "storeAndForwardConfiguration": { "timeToLiveSecs": 7200 } } } } } |