Uptime Kuma: 526 Error Code on Redirect When Using Custom HTTP Headers with Traefik Reverse Proxy

[zylxpl]

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Description

I am trying to monitor several services behind a Traefik reverse proxy using Uptime Kuma. Both Traefik and Uptime Kuma are on the same Docker network, and I am using Docker's DNS resolution to connect to the Traefik container by specifying its Docker DNS name (https://traefik/) in the URL field.

To ensure Traefik correctly handles requests to specific services, I am setting the HTTP header Host with the appropriate domain (e.g., whoami.example.com). Traefik also requires the correct Server Name Indication (SNI) or a matching domain to respond with the correct certificate. This setup works for most services. However, I encounter an issue with services that respond with a redirect. For these services, Uptime Kuma returns a 526 error code.

When manually checking these services, they work as expected. Additionally, if I specify the final path after redirects in the URL, it works correctly. This leads me to believe that Uptime Kuma might not be handling HTTP headers properly during redirects.

👟 Reproduction steps

1. Set Up Docker Network:

   Ensure that both Traefik and Uptime Kuma are on the same Docker network.

2. Configure Traefik:

   Set up Traefik with services that include redirects, e.g. Prometheus Ensure Traefik is configured to handle ssl requests.

3. Set Up Uptime Kuma:

   Deploy Uptime Kuma on the same Docker network. Add a new monitor in Uptime Kuma. In the URL field, specify the Docker DNS name of the Traefik container (e.g., https://traefik).

4. Set HTTP Header in Uptime Kuma:

   Set the HTTP header Host to the appropriate domain for the service (e.g., prometheus.example.com).

5. Test Service with Redirects:

   Ensure the service behind Traefik responds with a redirect. Observe that Uptime Kuma returns a 526 error code.

6. Manual Check:

   Manually access the service URL with the same Host header and note that it works correctly. Specify the final path after redirects in Uptime Kuma's URL field (e.g. /graph) and observe that it works correctly.

👀 Expected behavior

• Uptime Kuma should properly handle HTTP headers during redirects.
• When a service responds with a redirect, Uptime Kuma should follow the redirect while preserving the specified HTTP headers, including the Host header.
• The monitoring should succeed without returning a 526 error code, just as it does when the final path after redirects is specified directly in the URL field.
• Traefik should receive the correct SNI and matching domain to respond with the correct certificate for both initial and redirected requests.

😓 Actual Behavior

• When a service responds with a redirect, Uptime Kuma returns a 526 error code.
• Uptime Kuma does not seem to preserve the specified HTTP headers, including the Host header, during redirects.
• Manual checks of the services with the same Host header work correctly and do not return a 526 error code.
• Specifying the final path after redirects in the URL field of Uptime Kuma works correctly without any errors.
• Traefik is unable to provide the correct certificate during the redirect process due to the missing or incorrect SNI and matching domain.

🐻 Uptime-Kuma Version

1.23.13

💻 Operating System and Arch

Ubuntu 20.04 aarch64

🌐 Browser

Firefox

🖥️ Deployment Environment

• Runtime: Docker compose
• Database: sqlite/embedded
• Filesystem used to store the database on: ext4
• number of monitors: ~60

📝 Relevant log output

No response

[CommanderStorm]

What kind of a redirect+method are you using? https://developer.mozilla.org/en-US/docs/Web/HTTP/Redirections

[zylxpl]

In my case all of them are 302 Found redirections:

< HTTP/2 302 
< alt-svc: h3=":443"; ma=2592000
< content-type: text/html; charset=utf-8
< date: Tue, 30 Jul 2024 22:17:06 GMT
< location: /graph
< content-length: 29