Note
There are still some edge-cases when the plgd event couldn’t be published to the JetStream but it was stored to the EventStore. In such a case you need to identify that one event was lost and if needed, retrieve it using plgd gRPC Gateway.
By default, plgd hub services use NATS as an EventBus and MongoDB as an EventStore. Some use-cases require subscription directly to the internal messaging system instead of communicating with the plgd using its gateways. To simplify the data reconciliation and scale consumers easier, plgd supports JetStream technology as an alternative EventBus. JetStream is built on top of NATS, persisting all published events. Using JetStream as an EventBus allows you to access older, not yet processed messages without accessing the EventStore.
There are still some edge-cases when the plgd event couldn’t be published to the JetStream but it was stored to the EventStore. In such a case you need to identify that one event was lost and if needed, retrieve it using plgd gRPC Gateway.
More information about the JetStream can be found here.
Deployment of the JetStream as an EventBus will be controlled by a single configuration option available in the plgd HELM chart. This is currently WIP.
It’s required from you to create event streams before the JetStream can be used as the plgd EventBus. If streams are not created, plgd services won’t work.
Set env variable JETSTREAM=true of bundle
docker run -it --rm -e JETSTREAM=true --network=host -v `pwd`/.tmp/data:/data ghcr.io/plgd-dev/hub/bundle:latest)
Required nats-server 2.3+ Required nats client
Append jetstream configuration to nats.config of nats-server:
...
jetstream: {
store_dir: "$JETSTREAM_PATH"
// 1GB of memory
max_memory_store: 1073741824
// 10GB of memory
max_file_store: 10737418240
}
More information about nats-server configuration.
and start it:
nats-server -c nats.config
Setup events stream stream.json where all events of hub will be stored:
{
"name": "EVENTS", // A name for the Stream that may not have spaces, tabs, period (.), greater than (>), or asterisk (*).
"subjects": [ // A list of subjects to consume, supports wildcards.
"plgd.>"
],
"retention": "limits", // How message retention is considered, limits (default), interest or workQueue.
"max_consumers": -1, // How many Consumers can be defined for a given Stream, -1 for unlimited.
"max_msgs_per_subject": 0, // / How many messages may be in a subject of Stream, -1 for unlimited.
"max_msgs": -1, // How many messages may be in a Stream. Adheres to Discard Policy, removing oldest or refusing new messages if the Stream exceeds this size, -1 for unlimited.
"max_bytes": -1, // How many bytes the Stream may contain. Adheres to Discard Policy, removing oldest or refusing new messages if the Stream exceeds this number of messages, -1 for unlimited.
"max_age": 0, // Maximum age of any message in the Stream, expressed in nanoseconds, -1 for unlimited.
"max_msg_size": -1, // The largest message that will be accepted by the Stream. -1 for unlimited
"storage": "file", // The type of storage backend, file and memory
"discard": "old", // discard old messages when stream is full
"num_replicas": 1, // How many replicas to keep for each message in a clustered JetStream, maximum 5
"duplicate_window": 600000000000 // The window within which to track duplicate messages, expressed in nanoseconds.
}
More information about stream configuration.
And then apply the configuration to the nats-server via:
nats str add EVENTS --config /configs/jetstream.json
Creates NATS Server with JetStream enabled as a leaf node connection.
kubectl apply -f https://raw.githubusercontent.com/nats-io/k8s/master/nats-server/nats-js-leaf.yml
Now install the JetStream CRDs and Controller:
helm repo add nats https://nats-io.github.io/k8s/helm/charts/
helm install nats nats/nats --set nats.image=synadia/nats-server:nightly --set=nats.jetstream.enabled=true
helm install nack nats/nack --set=jetstream.nats.url=nats://nats:4222
Create one events stream
---
apiVersion: jetstream.nats.io/v1beta1
kind: Stream
metadata:
name: events
spec:
name: events
subjects: ["plgd.>"]
Set clients.eventBus.nats.jetstream to true value.
...
clients:
eventBus:
nats:
jetstream: true
...
plgd makes it simpler to build a successful IoT initiative – to create a proof of concept, evaluate, optimize, and scale.
