It appears that your reverse proxy set up is broken - Jenkins IIS - jenkins

Question

I cant seem to correctly setup Reverse Proxy for my Jenkins with IIS.
Everything works correctly however I cannot get that message to disappear! Running the "administrativeMonitor/hudson.diagnosis.ReverseProxySetupMonitor/testForReverseProxySetup" is not returning a 200.. but in fact a 404.
I also use the plugin Blue Ocean, I noticed that when running pipelines when accessing Jenkins via my Reverse Proxy, I cannot see the live updates!! I dug into this and found out that it usually is from a bad Revery Proxy setup. If I access jenkins via localhost, I can see Blue Ocean Pipeline updates live, so something must be setup wrong!
What I got:
Windows Server 2019 Datacenter
IIS 10
I have HTTPS setup, so my aim is: Go to jenkins.example.com, it will redirect to https://jenkins.example.com which in turn is a reverse proxy loading jenkins.
My web.config:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<rewrite>
<rules useOriginalURLEncoding="false">
<!-- Enforces redirection of all HTTP traffic to HTTPS -->
<rule name="Enforce HTTPS" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{HTTPS}" pattern="off" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}/{R:1}" redirectType="Permanent" />
</rule>
<rule name="ReverseProxyToLocalJenkinsRule" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{HTTPS}" pattern="on" />
</conditions>
<action type="Rewrite" url="http://jenkins.example.com:7070/{R:1}" />
<serverVariables>
<set name="X-Forwarded-Proto" value="https" />
<set name="X-Forwarded-Port" value="443" />
<set name="X-Forwarded-Host" value="{HTTP_HOST}" />
</serverVariables>
</rule>
</rules>
</rewrite>
<security>
<requestFiltering allowDoubleEscaping="true" />
</security>
</system.webServer>
<system.web>
<httpRuntime maxUrlLength="4096" />
</system.web>
</configuration>
This seems to be the best working reverse proxy I can obtain, following jenkins tutorials usually leads me to login issues (URL doubling up, i.e: example.com/https://example.com)
P.s, this is the latest windows server image out there and is a clean base build.
I ran through many tutorials however nothing has solved this issue, any advice is muchly appreciated.
I also want to point out that I have one server with Jenkins installed and IIS, Jenkins is accessible at localhost:7070 on the server locally. I also have edited my hosts file on the server to:
127.0.0.1 jenkins.example.com
Where the jenkins.example.com is an actual subdomain/domain pointing to the public IP of my server.
So when I ping: jenkins.domain.com on the server locally.. it returns 127.0.0.1. If I ping outside of that server, I.e.. on my PC, I get the public IP.
EDIT:
I have Application Request Routing installed and below is my config:

Answer 1

I just spent 6 hours of my life debugging this one, and I hope if some poor soul finds this page, as I did, my answer will be of some help. Almost identical situation to the original question, but for the sake of being thorough, I'll detail my exact situation, and my exact solution:
I am running a Windows Server 2019 Datacenter on AWS EC2
My EC2 instance lives under an Application Load Balancer which automatically redirects all http traffic to https, but forwards requests to the server using http only. That is, the user is always connected to the load balancer using https, but the load balancer connects to the server using only http
On that server, I am running Jenkins locally at localhost:8080
I want to reverse-proxy jenkins.mydomain.com to localhost:8080 without configuring SSL at the IIS level
I have read through ALL of the tutorials available on Jenkins' website, other websites with similar "IIS Jenkins Reverse Proxy" tutorials, and all related StackOverflow articles. NONE have solved my issue, and most want you to configure an SSL cert at the IIS level.
Also, I was getting the same mysterious error of the URL doubling up like jenkins.mydomain.com/"http://jenkins.mydomain.com:80"
Here is my exact configuration that solved the issue:
Obviously, you need to configure everything on AWS correctly. If you're not using AWS, make sure that your configuration is comparable.
EC2 Instance with security policy allowing incoming connections on port 80
Application Load Balancer redirects http requests to https, and forwards https requests to your EC2 instance on port 80
Application Load Balancer configured with SSL certificate
DNS configured to direct jenkins.mydomain.com to your Application Load Balancer
As with other tutorials, you must have ARR installed for IIS
UNLIKE other tutorials, do NOT add 127.0.0.1 jenkins.mydomain.com to your hosts file. If you have added it, remove it.
In IIS, Application Request Routing Cache > Server Proxy Settings
Enable Proxy: checked
Reverse rewrite host in response headers: checked
THIS DIFFERS FROM OTHER TUTORIALS, AND IS ULTIMATELY THE KEY THAT CAUSED MY SETUP TO WORK
In IIS, Default Website > Request Filtering > Edit Feature Settings
Allow Double Escaping: checked
In IIS, Default Website > URL Rewrite > Add Rule(s) > Blank Rule
Name: Jenkins Rewrite
Pattern: (.*)
Conditions: {HTTP_HOST} matches .*jenkins.mydomain.com.*
Server Variables: None
Action: Rewrite http://localhost:8080{UNENCODED_URL}
Note that THERE IS NO NEED to include an http to https redirect rule here. If you have one, I don't think it'll hurt anything, but don't get caught up by thinking this is important, as other tutorials suggest.
In IIS, Configuration Editor > system.webServer/rewrite/rules
useOriginalURLEncoding: False
In Jenkins (which you may need to access via loacalhost:8080 at first), Manage Jenkins > Configure System
Jenkins URL: https://jenkins.mydomain.com/
In Jenkins, Manage Jenkins > Configure Global Security
Enable Proxy Compatibility: checked
And that's it! It's possible that some of those steps (especially 9 and 10) may be unnecessary, but in the process of getting to where I am now, those values were ALREADY set, and once it started working I didn't want to change ANYTHING!
Again, the major breakthrough for me was to ENABLE "Reverse rewrite host in response headers".
Edit: Also, by the way, once you get everything working, feel free to just hit the "Disable" button on the Jenkins warning about your reverse proxy configuration being messed up. I think that this situation, and the resulting configuration to make it work, is so non-standard that Jenkins doesn't recognize that it is, in fact, working.