Basic monitoring with curl and jenkins/gitlab

So you just finished your super webapp/api and it’s already going live. I’ll show you a simple way to add a basic monitoring on your server without adding a new dedicated app to do the task, using only your CI/CD

The scripts

Say you want to check if your app responds with an HTTP 200. The following command will exit with error if so:

curl — silent — show-error — fail https://my-webapp.fr/

If you want to verify that a specific endpoint respond with a json object containing a predefined number of elements. We’re using jq:

#/bin/sh
nbElements=$(curl https://my-webapp.fr/api/endpoint | jq length)
echo $nbElements
if [ $nbElements -eq 2 ]; then
    echo "No errors, the list of nbElements is 2 as expected"
    exit 0;
else
    echo "Oops, something went wrong, nbElements should have 2 elements and only $nbElements were received..."
    exit 1;
fi

Monitor with Jenkins

Using Jenkins you can create a specific job that you will configure to run every (minute/5 minutes.. you decide)

jenkins

And simply add new build steps with the commands you want to execute:

jenkins

Specify a way of being notified if one of the scripts fail, email, slack etc.. and you’re done with this simple solution to monitor your service is up and running.

Seeing it fails…

You should never have faith in a test you haven’t seen fail…

So playing with my server I received the following mail when the test began to exit 1

+ curl https://mywebpp.fr/api/endpoint
+ jq length
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0100   568  100   568    0     0  10281      0 --:--:-- --:--:-- --:--:-- 10327
+ nbElement=1
+ echo 1
1
+ [ 2 -eq 10 ]
+ echo Oops, something went wrong, nbElement should have 2 elements and only 1 were received...
Oops, something went wrong, urbanAreas should have 2 elements and only 1 were received...
+ exit 1
Build step 'Exécuter un script shell' marked build as failure

Monitor with Gitlab

You will be using the Scheduled Pipelines of Gitlab:

jenkins

You need to add a specific stage for your monitoring tasks and exclude the other stages from being executed by the scheduled task

stages:
  - test
  - release
  - monitoring
test:
  stage: test
  except:
    - schedules
  script:
    - mvn test
release:
  stage: release
  except:
    - schedules
  script:
    - docker build --pull -t $PROJECT_RELEASE_IMAGE node/
    - docker push $PROJECT_RELEASE_IMAGE
monitoring:
  stage: monitoring
  only:
    - schedules
  script:
    - curl - silent - show-error - fail https://my-webapp.fr/
    - chmod +x /root/scripts/monitoring.sh     
    - ./sh /root/scripts/monitoring.sh

The downside of this last solution is that it will pollute your pipelines..

See you on twitter: m4nu56