KEDA scalers can both detect if a deployment should be activated or deactivated, and feed custom metrics for a specific event source.
Currently available scalers for KEDA
ActiveMQ
ActiveMQ Artemis
Apache Kafka
AWS CloudWatch
AWS Kinesis Stream
AWS SQS Queue
Azure Application Insights
Azure Blob Storage
Azure Event Hubs
Azure Log Analytics
Azure Monitor
Azure Pipelines
Azure Service Bus
Azure Storage Queue
Cassandra
CPU
Cron
Datadog
Elasticsearch
External
External Push
Google Cloud Platform‎ Pub/Sub
Graphite
Huawei Cloudeye
IBM MQ
InfluxDB
Kubernetes Workload
Liiklus Topic
Memory
Metrics API
MongoDB
MSSQL
MySQL
NATS Streaming
New Relic
OpenStack Metric
OpenStack Swift
PostgreSQL
Predictkube
Prometheus
RabbitMQ Queue
Redis Lists
Redis Lists (supports Redis Cluster)
Redis Lists (supports Redis Sentinel)
Redis Streams
Redis Streams (supports Redis Cluster)
Redis Streams (supports Redis Sentinel)
Selenium Grid Scaler
Solace PubSub+ Event Broker