Today I was looking at the internal struct that ends up being filled as the result of parsing the Docker Registry configuration, and doing that I found that in the
master branch of the repository there’s already support for metrics scraping by Prometheus (see configuration.go), something that used to be only available in OpenShift (see openshift/origin issue).
It surprised me that this addition came not super recently:
commit e3c37a46e2529305ad6f5648abd6ab68c777820a Author: tifayuki <firstname.lastname@example.org> Date: Thu Nov 16 16:43:38 2017 -0800 Add Prometheus Metrics at the first iteration, only the following metrics are collected: - HTTP metrics of each API endpoint - cache counter for request/hit/miss - histogram of storage actions, including: GetContent, PutContent, Stat, List, Move, and Delete Signed-off-by: tifayuki <email@example.com>
What about giving it a try?
So, first, start by building an image right from the
# Clone the Docker registry repository git clone https://github.com/docker/distribution # Build the registry image using the provided Dockerfile # that lives right in the root of the project. # # Here I tag it as `local` just to make sure that we # don't confuse it with `registry:latest`. docker build --tag registry:local .
With the image built using the latest code, tailor a configuration that enables the exporter:
version: 0.1 log: level: "debug" formatter: "json" fields: service: "registry" storage: cache: blobdescriptor: "inmemory" filesystem: rootdirectory: "/var/lib/registry" http: addr: ":5000" debug: addr: ":5001" prometheus: enabled: true path: "/metrics" headers: X-Content-Type-Options: [ "nosniff" ]
Run the registry with this configuration and note how
:5001/metrics will provide you with the metrics you expect.
# Make a request to the metrics endpoint and filter the # output so we can see what the metrics descriptions are. # # ps.: each of those metrics end up expanding to multiple # dimensions via labels. curl localhost:5001/metrics --silent | ag registry_ | ag HELP HELP registry_http_in_flight_requests The in-flight HTTP requests HELP registry_http_request_duration_seconds The HTTP request latencies in seconds. HELP registry_http_request_size_bytes The HTTP request sizes in bytes. HELP registry_http_requests_total Total number of HTTP requests made. HELP registry_http_response_size_bytes The HTTP response sizes in bytes. HELP registry_storage_action_seconds The number of seconds that the storage action takes HELP registry_storage_cache_total The number of cache request received
Wanting to see how useful these metrics can be, I set up an environment in AWS where there’s an EC2 instance with a registry instance that’s backed by an S3 bucket as the storage tier (you can check more about how to achieve it here: How to set up a private docker registry using AWS S3).
With the registry up, it was now a matter of having Prometheus and Grafana running locally so I could start making some queries:
version: '3.3' services: # Create a "pod-like" container that will serve as both the # network entrypoint for both of the containers as well as # provide a common ground for them to communicate over localhost # (given that they'll share the same network namespace). pod: container_name: 'pod' ports: - '9090:9090' - '3000:3000' image: 'alpine' tty: true grafana: container_name: 'grafana' depends_on: [ 'pod' ] network_mode: 'service:pod' image: 'grafana/grafana:5.2.0-beta3' restart: 'always' prometheus: container_name: 'prometheus' depends_on: [ 'pod' ] network_mode: 'service:pod' image: 'prom/prometheus' restart: 'always' volumes: - './prometheus.yml:/etc/prometheus/prometheus.yml'
prometheus is making use of a local configuration under
./prometheus.yml, this one looked like the following:
global: scrape_interval: '15s' evaluation_interval: '15s' scrape_timeout: '10s' scrape_configs: - job_name: 'prometheus' static_configs: - targets: [ 'localhost:9090' ] - job_name: 'registry' # Here I just specified the public IP address of the # EC2 instance that I had holding the registry at that # time. # # Naturally, you wouldn't keep it open like this. static_configs: - targets: [ '188.8.131.52:5001' ]
Now, to reproduce the panel showed in the beginning, head over to our grafana dashboard and create a heatmap panel with the following query:
If you have any questions or found something odd, please let me know! I’m cirowrc on Twitter.
Have a good one!