use the requested Host header in the proxied request

[ahmadnassri]

When setting up Kong in-front of an API service that relies on the Host header for routing (e.g. Kong itself), Kong uses the target_url in the proxied request.

it should either:

• have a flag to use the client-side Host header all the way through (perhaps this should be the default?)
• allow the Host header to be set at the time of creation as an additional property of the API object.

alternatively the request-transformer plugin could be used here, however, currently attempting to overwrite the Host header with request-transformer does nothing. (see #445)

detailed example:

┌────────────────────┐
│      Consumer      │
└────────────────────┘
           │
           ▼
┌────────────────────┐
│GET / HTTP/1.1      │
│Accept: */*         │
│Host: mockbin.com   │
└────────────────────┘
           │             ┌─────────────────────────────────────────┐
           ▼             │{                                        │
┌────────────────────┐   │  "public_dns": "mockbin.com",           │
│        Kong        │───│  "target_url": "http://173.236.235.78/" │
└────────────────────┘   │}                                        │
           │             └─────────────────────────────────────────┘
           ▼
┌────────────────────┐
│GET / HTTP/1.1      │
│Accept: */*         │
│Host: 173.236.235.78│
└────────────────────┘
           │             ┌─────────────────────────────────────────┐
           ▼             │{                                        │
┌────────────────────┐   │  "public_dns": "mockbin.com",           │
│        Kong        │───│  "target_url": "http://mockbin.org/"    │
└────────────────────┘   │}                                        │
           │             └─────────────────────────────────────────┘
           ▼
┌────────────────────┐
│  API not found :(  │
└────────────────────┘

           x
┌────────────────────┐
│    mockbin.org     │
└────────────────────┘

[subnetmarco]

I can easily fix this, but it may lead to some problems. I believe the reason we decided to change the Host header to reflect the target url's host, is because it created issues with the Virtual Host resolution: some servers that handle more than one host, use the Host header to determine the Virtual Host that should process the request.

We need to better test this. If we find out that it can cause problems, then this needs to be a flag when adding the API, like preserve_host = true | false.

[subnetmarco]

Specifically, we need to understand if this is really required: https://github.com/Mashape/kong/blob/master/kong/resolver/access.lua#L179

The fix to this issue would be to comment that line, and add the following nginx directive before the proxy_pass instruction:

proxy_set_header Host $host;

[ahmadnassri]

as mentioned, I believe both solutions are valid (in different scenarios) therefore, should be flag ... or a feature of request transform plugin

[subnetmarco]

I have added the preserve_host flag (default false) when adding a new API.