Home » DevOps » Simple retry until with WGet

About Romain Manni-Bucau

Romain is a senior software engineer with a deep background on technical stacks from the standalone to cloud native applications without forgetting Bi Data. He also contributes a lot to the Open Source ecosystem (Apache, Yupiik, ...)

Simple retry until with WGet


Ensure some commands are executed only when a service is up is a common need of
docker-compose or even
Kubernetes when using some container to setup some state. If you can use
wget, it has almost this feature built-in.

For a HTTP backend, awaiting it is ready – most of the time its healthcheck too – is often testing a resource returns a HTTP 200 (can be a version endpoint, an asset or whatever simple and not writing anything).

There are a ton of curl based script doing some while loops to solve that, even some custom go, node scripts but if you have wget if you base image, it is actually quite trivial since wget supports retries:

wget \
  --no-check-certificate \ (1)
  --read-timeout=30 --timeout=30 \ (2)
  --retry-connrefused \ (3)
  --waitretry=5 \ (4)
  --tries=60 \ (5)
  "https://$MY_SERVICE_HOST:$MY_SERVICE_PORT/some/resource" (6)
1(optional) ignore SSL errors, depends your environment,
2the common request timeouts, just ensure to fail if it hangs,
3consider a connect refused as a retryable case,
4wait 5s before retrying again – depends how fast/slow is your backend,
5retry max 60 times (so 5 minutes max with the wait configuration),
6the test endpoint configured using Kubernetes service environment variables (for a my service in this sample).

Adding this kind of wget at the beginning of a script or custom entrypoint.sh enables to ensure some dependency are available or at least await for them a few before giving up. The big advantage compared to what we find on the net is that it does not need any shell knowledge with loops or whatever to implement it which is always a concern in a team but the assumption you have wget in the base image is required.

curl has similar option if you have a recent enough version:

curl \
  --connect-timeout 30 --max-time 30 \
  --retry-connrefused \
  --retry-all-errors \
  --retry 60 \
  --retry-delay 5 \
  --retry-max-time 300 \
  "https://$MY_SERVICE_HOST:$MY_SERVICE_PORT/some/resource"

if you need a compatible debian based image you can use rmannibucau/curl:bookworm-slim@sha256:208599dbcf1d2e673a8f6f463093b9264e52c02ee05e99ed35ba3bdbdf416704.

Published on Java Code Geeks with permission by Romain Manni, partner at our JCG program. See the original article here: Simple retry until with WGet

Opinions expressed by Java Code Geeks contributors are their own.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you our best selling eBooks for FREE!

 

1. JPA Mini Book

2. JVM Troubleshooting Guide

3. JUnit Tutorial for Unit Testing

4. Java Annotations Tutorial

5. Java Interview Questions

6. Spring Interview Questions

7. Android UI Design

 

and many more ....

 

Receive Java & Developer job alerts in your Area

I have read and agree to the terms & conditions

 

Subscribe
Notify of
guest

This site uses Akismet to reduce spam. Learn how your comment data is processed.

0 Comments
Inline Feedbacks
View all comments