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How-to.md

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How to work with Chronos

Pre-requisites

For starting the delay queue process, Chronos expects a DB in Postgres and two topics one for input and other for publishing the messages after delay to be already created. The names of the topics and DB should be passed as env variables mentioned in Env vars Input messages with headers

  • chronosMessageId
  • chronosDeadline

will be processed for a delay depending on deadline header to be published on the output topic after the delay is acheived.

Messages missing any of two above mentioned headers will be discarded.

Run Binary

  1. Start Kafka brokers and Postgres server on local dev machine
  2. Delete any existing .env file, use make withenv RECIPE=run

Run Chronos docker image

Using docker-compose docker conatiner can host Chronos image with mentioned env variables for Kafka, PG and Chronos configuration variables.

Use make withenv RECIPE=docker.up

ENV vars

All the required configurations for Chronos can be passed in environment variables mentioned below

Required Vars

Env Var Example Value
KAFKA_HOST "localhost"
KAFKA_PORT 9093
KAFKA_CLIENT_ID "chronos"
KAFKA_GROUP_ID "chronos"
KAFKA_IN_TOPIC "chronos.in"
KAFKA_OUT_TOPIC "chronos.out"
KAFKA_USERNAME
KAFKA_PASSWORD
PG_HOST localhost
PG_PORT 5432
PG_USER admin
PG_PASSWORD admin
PG_DATABASE chronos_db
PG_POOL_SIZE 50

Optional Vars

These values are set to fine tune performance Chrono in need, refer to Chronos

Env Var Default Value
MONITOR_DB_POLL 5 sec
PROCESSOR_DB_POLL 5 milli sec
TIMING_ADVANCE 0 sec
FAIL_DETECT_INTERVAL 10 sec
HEALTHCHECK_FILE healthcheck/chronos_healthcheck

Observability

At this time Chronos supports Http protocol based connectivity to the Otel collector. By providing following env variables for connecting to the Otel collector instance, traces will appear under the service name mentioned.

Env var Default Value
OTEL_SERVICE_NAME Chronos
OTEL_TRACES_EXPORTER otlp
OTEL_EXPORTER_OTLP_TRACES_ENDPOINT "http://localhost:4318/v1/traces"
OTEL_EXPORTER_OTLP_PROTOCOL "http/json"

Chronos Images

Two images are published for each RELEASE

  • migrations image
  • chornos image