SSO & external avatars

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The discussion revolves around optimizing avatar performance when using SSO in Discourse. mentalstring notes that avatars are being proxied through Discourse’s backend instead of being served directly from their external URLs, even when stored in object storage like S3. This causes unnecessary server load. DrewH suggests disabling download_remote_images_to_local, but mentalstring clarifies this only affects post images. Falco explains that the external_system_avatars_url setting can enable direct serving for certain formats, but this doesn’t apply to S3-hosted avatars. mentalstring revisits the issue, clarifying that SSO avatars are already stored in object storage but are still proxied via Discourse, unlike regular avatars which are served directly. They question why a direct CDN link isn’t used and note that a redirect setting exists but adds latency. Falco confirms that by default, Discourse proxies avatars, but the DISCOURSE_REDIRECT_AVATAR_REQUESTS=1 setting can enable direct serving, though it may not be ideal for SSO cases.

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When using SSO with sso overrides avatar: true, Discourse seems to download the avatar and always serve it locally instead of linking directly to the URL provided.

Would it make more sense to allow avatars to serve directly from the avatar_url provided? As is, for each avatar shown it hits Discourse backend somewhat needlessly. Perhaps this could be a SSO option?

If the concern is that avatars may go missing, that could be handled with the image onerror event that fallback’s src to the locally downloaded copy (or show a default one). What I don’t know is if too large avatars images can be constrained with CSS alone.

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Allow polling avatar from URI
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I believe disabling download_remote_images_to_local should solve your issue, although this will also serve images within posts remotely instead of locally.

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That seems to be only for images in posts — or perhaps for local avatar too, when they are not overwritten by SSO.

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4

Interesting. I know that the OIDC Plugin allows you to override email on every login, maybe something like this would be possible for avatar’s being overwritten by SSO as well.

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If the SSO avatar is in the format of https://central.avatar.service/<username> you can use the external_system_avatars_url site setting to get this feature.

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It’s not in our case (they are served from S3) — and it’s unlikely to usually be in that format so that it can be efficiently cached.

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Following up on this a couple of years later as I think I previously misunderstood something, however, I still think there is still an easy win here for performance.

Previously I thought the avatars were being stored locally (Discourse server itself) and was wondering why they weren’t served directly from the SSO external avatar URL instead of hitting Discourse. However, after some poking, I see now that external avatars coming from SSO are already uploaded to the object storage (e.g. S3) and in the required multiple sizes.

So, if I understand correctly, currently Discourse is proxying avatars from the object storage to the client. However, this behavior seems specific to when using SSO external avatars since avatars here in meta are coming directly from the (CDN’ed) object storage. But when using SSO with external URLs, the avatar URLs are in the form

https://discourse-host/user_avatar/discourse-host/{username}/{size}/{uploadid}_{version}.png

where it hits rails for every avatar displayed (before being cached by the client).

And if I understand the code, there’s even a setting to allow a redirect instead of proxying it, but at that point it already hit rails and the redirect only adds up time to the load time for the client.

Wouldn’t it be faster to just link avatars to the object storage (potentially serving it from a CDN) while freeing some rails resources at the same time? /cc @Falco

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That’s not the case. By default, Discourse will proxy requests for avatars, as you see on your site.

However, last year, we introduced a setting that can be enabled via the ENV DISCOURSE_REDIRECT_AVATAR_REQUESTS=1 to trigger the behavior you see here.

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