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Update Preamble documentation for clusters with mixed request sources and loadbalancer chains

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Summary:
Fixes T11487. Improve documentation for three situations:

  - When you configure a cluster behind a load balancer, all requests are trusted but not all have an "X-Forwarded-For" header. Change the suggested snippet to read this header only if it exists.
  - When a request goes through a series of load balancers (as with a CDN) they can end up writing a list of IPs to the header. Parse these.
  - Remove the "rate limiting" stuff -- this got disabled/removed a long time ago and is misleading/incorrect.

Test Plan: Read documentation.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11487

Differential Revision: https://secure.phabricator.com/D16403
This commit is contained in:
epriestley 2016-08-16 15:46:47 -07:00
parent 05f7227329
commit a35b03ac6a
1 changed files with 41 additions and 44 deletions
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85
src/docs/user/configuration/configuring_preamble.diviner
View file

@ -4,7 +4,8 @@
Adjust environmental settings (SSL, remote IP, rate limiting) using a preamble
script.
= Overview =
Overview
========
If Phabricator is deployed in an environment where HTTP headers behave oddly
(usually, because it is behind a load balancer), it may not be able to detect
@ -37,27 +38,52 @@ If present, this script will be executed at the very beginning of each web
request, allowing you to adjust the environment. For common adjustments and
examples, see the next sections.
= Adjusting Client IPs =
Adjusting Client IPs
====================
If your install is behind a load balancer, Phabricator may incorrectly detect
all requests as originating from the load balancer, rather than from the correct
client IPs. If this is the case and some other header (like `X-Forwarded-For`)
is known to be trustworthy, you can overwrite the `REMOTE_ADDR` setting so
Phabricator can figure out the client IP correctly:
all requests as originating from the load balancer, rather than from the
correct client IPs.
If this is the case and some other header (like `X-Forwarded-For`) is known to
be trustworthy, you can read the header and overwrite the `REMOTE_ADDR` value
so Phabricator can figure out the client IP correctly.
You should do this //only// if the `X-Forwarded-For` header is known to be
trustworthy. In particular, if users can make requests to the web server
directly, they can provide an arbitrary `X-Forwarded-For` header, and thereby
spoof an arbitrary client IP.
The `X-Forwarded-For` header may also contain a list of addresses if a request
has been forwarded through multiple loadbalancers. Using a snippet like this
will usually handle most situations correctly:
```
name=Overwrite REMOTE_ADDR with X-Forwarded-For
<?php
$_SERVER['REMOTE_ADDR'] = $_SERVER['HTTP_X_FORWARDED_FOR'];
// Overwrite REMOTE_ADDR with the value in the "X-Forwarded-For" HTTP header.
// Only do this if you're certain the request is coming from a loadbalancer!
// If the request came directly from a client, doing this will allow them to
// them spoof any remote address.
// The header may contain a list of IPs, like "1.2.3.4, 4.5.6.7", if the
// request the load balancer received also had this header.
if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
$forwarded_for = $_SERVER['HTTP_X_FORWARDED_FOR'];
if ($forwarded_for) {
$forwarded_for = explode(',', $forwarded_for);
$forwarded_for = end($forwarded_for);
$forwarded_for = trim($forwarded_for);
$_SERVER['REMOTE_ADDR'] = $forwarded_for;
}
}
```
You should do this //only// if the `X-Forwarded-For` header is always
trustworthy. In particular, if users can make requests to the web server
directly, they can provide an arbitrary `X-Forwarded-For` header, and thereby
spoof an arbitrary client IP.
= Adjusting SSL =
Adjusting SSL
=============
If your install is behind an SSL terminating load balancer, Phabricator may
detect requests as HTTP when the client sees them as HTTPS. This can cause
@ -76,38 +102,9 @@ $_SERVER['HTTPS'] = true;
You can also set this value to `false` to explicitly tell Phabricator that a
request is not an SSL request.
= Adjusting Rate Limiting =
Phabricator performs coarse, IP-based rate limiting by default. In most
situations the default settings should be reasonable: they are set fairly high,
and intended to prevent only significantly abusive behavior.
However, if legitimate traffic is being rate limited (or you want to make the
limits more strict) you can adjust the limits in the preamble script.
```
name=Adjust Rate Limiting Behavior
<?php
// The default is 1000, so a value of 2000 increases the limit by a factor
// of 2: users will be able to make twice as many requests before being
// rate limited.
// You can set the limit to 0 to disable rate limiting.
PhabricatorStartup::setMaximumRate(2000);
```
By examining `$_SERVER['REMOTE_ADDR']` or similar parameters, you could also
adjust the rate limit dynamically: for example, remove it for requests from an
internal network, but impose a strict limit for external requests.
Rate limiting needs to be configured in this way in order to make it as cheap as
possible to activate after a client is rate limited. The limiting checks execute
before any libraries or configuration are loaded, and can emit a response within
a few milliseconds.
= Next Steps =
Next Steps
==========
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