urlwatch

README

URLWatch

Service for watching urls for liveness.

Usage:
  urlwatch start [flags]

Flags:
  -h, --help              help for start
  -i, --interval string   how long to wait between checks (default "30s")
  -p, --port int          port the metrics will be servied from (default 80)
  -t, --timeout string    how long to wait before cancelling a connectino request (default "2s")
      --url strings       provide each url that needs to be tracked

How it works

This service monitors urls by instantiating a Watcher goroutine for each url provided at runtime. A go time.Ticker is used to inform the Watcher when it needs to perform its duty. At that time each Watcher sends a GET request to its url. If the response code is 200 and the response time is less than the timeout the url is considered up. Any error that occurs during the request will cause a code of 0 and a response time of 0.

Along with the Watchers, watchurl also instantiates a prometheus server and a metrics catcher service. The Metrics Catcher shares a channel with the Watchers so it can receive the results of url checks. Once received, the metrics catcher sends the metric data to the prometheus client to be served via the /metrics endpoint later.

Last but not least, a final thread is spun off to listen for OS signals like ctrl+c from the user. When this occurs the signal listener uses channels to the other concurrent processes to signal them to stop so the watcherurl application can cleanly exit.

Run locally

$ go run main.go start --url https://httpstat.us/200 --url https://httpstat.us/503 --port 8080
starting watcher service
watching urls:
https://httpstat.us/200
https://httpstat.us/503
2020/11/03 23:26:00 checking url:  https://httpstat.us/200
2020/11/03 23:26:00 checking url:  https://httpstat.us/503

Deploy

The easy way

kubectl apply -f deploy/deploy.yaml
# wait 30 seconds or watch the pod logs until the first url checks occur
kubectl port-forward deploy/urlwatch 8080:80

now visit http://localhost:8080/metrics in your browser

The hard way

Build docker image

docker build -t your_registry/account_name/urlwatch:1 .
docker push your_registry/account_name/urlwatch:1

Helm deploy

$ helm install urlwatch deploy/urlwatch --set image.repository=your_registry/account_name/urlwatch --set image.tag=1
NAME: urlwatch
LAST DEPLOYED: Tue Nov  3 22:01:46 2020
NAMESPACE: default
STATUS: deployed
REVISION: 1
NOTES:
1. Get the application URL by running these commands:
  export POD_NAME=$(kubectl get pods --namespace default -l "app.kubernetes.io/name=urlwatch,app.kubernetes.io/instance=urlwatch" -o jsonpath="{.items[0].metadata.name}")
  echo "Visit http://127.0.0.1:8080 to use your application"
  kubectl --namespace default port-forward $POD_NAME 8080:80

Test

go test -cover -v ./...