What is it?

Event-scheduler is a high available strongly consistent (powered by raft) high performance application designed to receive messages from the source queue and release them to the target queue at requested time, specified in message attribute. You can have many number of channels (single source to single destination) at the same time (manageable through API)

Performance

Application is able to find messages which are ready for dispatch in constant time and extract them in O(log N) time, where N is total number of messages in a channel

Currently supported queue drivers

1. Google Pubsub

Pubsub queue configuration

1. Add available_at (timestamp in seconds) attribute to your pubsub messages to tell the scheduler when you want them to be released to the target queue
2. Add Pubsub subscription with a filter "attributes:available_at" and use it as source queue
3. Create target topic (you can use same topic as source topic but make sure your application's subscription has the filter "NOT attributes:available_at"). So event-scheduler will consume scheduled only messages, and your app will consume real-time messages only

Scheduler configuration

Event scheduler can be configured via env vars:

Env var name	Type	Default Value	Description
LOG_FORMAT	string	text	log format output: json, text, gcp
LOG_LEVEL	string	info	log verbosity
LISTENER_DRIVER	string	pubsub	source (scheduled) messages queue driver
PUBSUB_LISTENER_PROJECT_ID	string		(*) source queue pubsub project id
PUBSUB_LISTENER_SUBSCRIPTION_ID	string		(*) source queue pubsub subscription id
PUBSUB_LISTENER_KEY_FILE	string		(*) path to pubsub service account access key file for source queue
PUBLISHER_DRIVER	string	pubsub	(*) target messages queue driver
PUBSUB_PUBLISHER_PROJECT_ID	string		(*) target queue pubsub project id
PUBSUB_PUBLISHER_TOPIC_ID	string		(*) target queue pubsub topic id
PUBSUB_PUBLISHER_KEY_FILE	string		(*) path to pubsub service account access key file for target queue
STORAGE_PATH	string	storage	path for persistent data storage
CLUSTER_NODE_HOST	string	localhost	node host, should be accessible from other cluster nodes
CLUSTER_NODE_PORT	string	5559	node port for interaction with other cluster nodes
CLUSTER_INITIAL_NODES	string	localhost:5559	comma separated list of cluster nodes
API_PORT	string	5569	api port

[*] - initial value for default channel, can be omitted and configured later using API

Execution

go run app/main.go

API overview

API is served on the port defined in API_PORT env var. You can use any node for API calls. Application will be able to automatically forward API requests to the leader node when needed

Cluster management API

Get cluster status

curl -XGET "http://event-scheduler:5569/cluster" --header "Content-type: application/json"

Add node

curl -XPOST "http://event-scheduler:5569/cluster" --header "Content-type: application/json" -d '{"node_addr": "node4:5559"}'

Remove node

curl -XDELETE "http://event-scheduler:5569/cluster" --header "Content-type: application/json" -d '{"node_addr": "node4:5559"}'

Channel management API

Get channels

curl -XGET "http://event-scheduler:5569/channels" --header "Content-type: application/json"

Add channel

curl -XPOST "http://event-scheduler:5569/channels" --header "Content-type: application/json" -d '{"source":{"driver":"pubsub","config":{"project_id":"test_project","subscription_id":"test_subscription","key_file":"test_key_file"}},"destination":{"driver":"pubsub","config":{"project_id":"test_project","topic_id":"test_topic","key_file":"test_key_file"}}}'

Update channel

curl -XPATCH "http://event-scheduler:5569/channels/{channel_id}" --header "Content-type: application/json" -d '{"source":{"driver":"pubsub","config":{"project_id":"test_project","subscription_id":"test_subscription","key_file":"test_key_file"}},"destination":{"driver":"pubsub","config":{"project_id":"test_project","topic_id":"test_topic","key_file":"test_key_file"}}}'

Remove channel

curl -XDELETE "http://event-scheduler:5569/channels/{channel_id}" --header "Content-type: application/json"

Tests

go test -covermode=atomic ./...

Run with Kubernetes

# replace serviceaccount.json to the path to your service account key file with PubsubPermissions
kubectl create secret generic pubsubserviceaccount --from-file key.json=serviceaccount.json
# feel free to adjust env vars inside deployment manifest
kubectl apply -f ./event-scheduler/kubernetes/deployment

Future / Roadmap (Unordered)

• Multi-channel support + channel API
• High availability
• Persistent storage
• Test cases
• Docker build
• Sample kubernetes deployment
• Message compression
• Prometheus metrics
• Horizontal scaling / Sharding
• Helm package