logspout-kafka

A Logspout adapter for writing Docker container logs to Kafka topics.

usage

With container-logs as the Kafka topic for Docker container logs, we can direct all messages to Kafka using the logspout Route API:

curl http://container-host:8000/routes -d '{
  "adapter": "kafka",
  "filter_sources": ["stdout" ,"stderr"],
  "address": "kafka-broker1:9092,kafka-broker2:9092/container-logs"
}'

message template configuration

The default behavior is to route the raw message to Kafka. This adapter provides a mechanism for customizing the template to include additional metadata via the KAFKA_TEMPLATE environment variable. Golang's text/template package is used for templating, where the model available for templating is the Message struct.

The following example KAFKA_TEMPLATE configuration appends additional metadata to each log message received:

KAFKA_TEMPLATE="time=\"{{.Time}}\" container_name=\"{{.Container.Name}}\" source=\"{{.Source}}\" data=\"{{.Data}}\""

Example input and output

Hello World

time="2015-06-23 09:54:55.241951004 +0000 UTC" container_name="/hello_container" source="stdout" data="Hello World"

route configuration

If you've mounted a volume to /mnt/routes, then consider pre-populating your routes. The following script configures a route to send standard messages from a "cat" container to one Kafka topic, and a route to send standard/error messages from a "dog" container to another topic.

cat > /logspout/routes/cat.json <<CAT
{
  "id": "cat",
  "adapter": "kafka",
  "filter_name": "cat_*",
  "filter_sources": ["stdout"],
  "address": "kafka-broker1:9092,kafka-broker2:9092/cat-logs"
}
CAT

cat > /logspout/routes/dog.json <<DOG
{
  "id": "dog",
  "adapter": "kafka",
  "filter_name": "dog_*",
  "filter_sources": ["stdout", "stderr"],
  "address": "kafka-broker1:9092,kafka-broker2:9092/dog-logs"
}
DOG

docker run --name logspout \
  -p "8000:8000" \
  --volume /logspout/routes:/mnt/routes \
  --volume /var/run/docker.sock:/tmp/docker.sock \
  gettyimages/example-logspout

The routes can be updated on a running container by using the logspout Route API and specifying the route id "cat" or "dog".

build

logspout-kafka is a custom logspout module. To use it, create an empty Dockerfile based on gliderlabs/logspout and include this logspout-kafka module in a new modules.go file.

The following example creates an almost-minimal logspout image capable of writing Docker container logs to Kafka topics:

cat > ./Dockerfile.example <<DOCKERFILE
FROM gliderlabs/logspout:master

ENV KAFKA_COMPRESSION_CODEC snappy
DOCKERFILE

cat > ./modules.go <<MODULES
package main
import (
  _ "github.com/gliderlabs/logspout/httpstream"
  _ "github.com/gliderlabs/logspout/routesapi"
  _ "github.com/gettyimages/logspout-kafka"
)
MODULES

docker build -t gettyimages/example-logspout -f Dockerfile.example .

More info about building custom modules is available at the logspout project: Custom Logspout Modules