Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

Broken image tags when image is changed with rendition caching enabled

See original GitHub issue

Issue Summary

With rendition caching enabled, changing an image results in broken image tags (old file paths remain cached).

Steps to Reproduce

  1. Start a new project with wagtail start myproject
  2. Enable rendition caching
  3. Edit home/ as follows
from django.db import models

from wagtail.core.models import Page
from wagtail.images.edit_handlers import ImageChooserPanel

class HomePage(Page):
    image = models.ForeignKey(
        'wagtailimages.Image', on_delete=models.SET_NULL, related_name='+', null=True, blank=True

    content_panels = Page.content_panels + [
  1. Edit home/templates/home/home_page.html as follows
{% extends "base.html" %}
{% load static wagtailimages_tags %}

{% block content %}
{% image page.image width-200 %}
{% endblock content %}
  1. Open the page in the frontend, ensure the rendition is cached
  2. Change the image in the Wagtail admin (Change image file)
  3. Reload the page from step 5, a broken image tag is now rendered because an old image path is still cached

I would expect the cache to be cleared when the image is changed.

  • I have confirmed that this issue can be reproduced as described on a fresh Wagtail project: no

Technical details

  • Python version: 3.8.2
  • Django version: 3.0.5
  • Wagtail version: 2.9.0

Issue Analytics

  • State:closed
  • Created 3 years ago
  • Comments:9 (2 by maintainers)

github_iconTop GitHub Comments

tomdysoncommented, Jun 2, 2020

Thank you very much for the report and investigations, @pascalw. I’m sorry for introducing this bug.

I think the cache key can be made robust enough by including the file hash, i.e.:

# images/, line 286
rendition_cache_key = "image-{}-{}-{}-{}".format(,

I’ve tested this successfully with file and focal point changes.

pascalwcommented, Jun 2, 2020

@tomdyson no need to apologize for bugs! (

I’m not sure though that only adding the file_hash to the cache key is a full solution. It indeed will work most of the time, but for example it doesn’t in this case:

  1. Upload an image
  2. Make sure renditions are cached
  3. Change the image (upload a new file)
  4. Change the image back to the previous file → Cache is poisoned

Now granted, this is a bit of an edge case but it’s annoying to recover from. Also if in the future new attributes or functionality are added to Images or Renditions, new scenario’s might be introduced where the cache is poisoned in a similar way.

What do you think about using signals to purge the cache when renditions are destroyed or updated? This seems pretty robust and cover all current and future cases, and we don’t have to add a column to the image table.

Something like this:

def post_delete_purge_cache(instance, **kwargs):
    transaction.on_commit(lambda: purge_rendition_cache(instance))

def register():
    Image = get_image_model()
    Rendition = Image.get_rendition_model()

    post_delete.connect(post_delete_purge_cache, sender=Rendition)
Read more comments on GitHub >

github_iconTop Results From Across the Web

Dispatcher caching issue while displaying ... - Adobe Support
If the image is first accessed from the mobile devices, then Untitled.jpg folder is created to cache the renditions image. Rendition images are ......
Read more >
publishing site - Image renditions not working anymore
1 Answer 1 ... Image Renditions will work if you first flush the blob cache and then do IISRESET (otherwise it will still...
Read more >
Image rendition issues in SharePoint on premise related to ...
Images do not load properly or load with full size that is without rendition. This can happen if Blob Cache is corrupted on...
Read more >
Angular: caching of images when using img ng-src in firefox ...
I used to use jQuery DOM manipulation (insertion of <img> tags) to show different images based on what the user clicked, and recently...
Read more >
Dispatcher caching issue while displaying the image ...
We are using the image renditions to display the images for different devices in Adobe Experience Manager(AEM). The HTML5 Adaptive image is used ......
Read more >

github_iconTop Related Medium Post

No results found

github_iconTop Related StackOverflow Question

No results found

github_iconTroubleshoot Live Code

Lightrun enables developers to add logs, metrics and snapshots to live code - no restarts or redeploys required.
Start Free

github_iconTop Related Reddit Thread

No results found

github_iconTop Related Hackernoon Post

No results found

github_iconTop Related Tweet

No results found

github_iconTop Related Post

No results found

github_iconTop Related Hashnode Post

No results found