How to Configure Symfony to Work behind a Load Balancer or a Reverse Proxy
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How to Configure Symfony to Work behind a Load Balancer or a Reverse Proxy
When you deploy your application, you may be behind a load balancer (e.g. an AWS Elastic Load Balancing) or a reverse proxy (e.g. Varnish for caching).
For the most part, this doesn't cause any problems with Symfony. But, when
a request passes through a proxy, certain request information is sent using
either the standard Forwarded
header or X-Forwarded-*
headers. For example,
instead of reading the REMOTE_ADDR
header (which will now be the IP address of
your reverse proxy), the user's true IP will be stored in a standard Forwarded: for="..."
header or a X-Forwarded-For
header.
If you don't configure Symfony to look for these headers, you'll get incorrect information about the client's IP address, whether or not the client is connecting via HTTPS, the client's port and the hostname being requested.
Solution: setTrustedProxies()
To fix this, you need to tell Symfony which reverse proxy IP addresses to trust and what headers your reverse proxy uses to send information:
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# config/packages/framework.yaml
framework:
# ...
# the IP address (or range) of your proxy
trusted_proxies: '192.0.0.1,10.0.0.0/8'
# trust *all* "X-Forwarded-*" headers
trusted_headers: ['x-forwarded-for', 'x-forwarded-host', 'x-forwarded-proto', 'x-forwarded-port', 'x-forwarded-prefix']
# or, if your proxy instead uses the "Forwarded" header
trusted_headers: ['forwarded']
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<!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:framework="http://symfony.com/schema/dic/symfony"
xsi:schemaLocation="http://symfony.com/schema/dic/services
https://symfony.com/schema/dic/services/services-1.0.xsd
http://symfony.com/schema/dic/symfony
https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">
<framework:config>
<!-- the IP address (or range) of your proxy -->
<framework:trusted-proxies>192.0.0.1,10.0.0.0/8</framework:trusted-proxies>
<!-- trust *all* "X-Forwarded-*" headers -->
<framework:trusted-header>x-forwarded-for</framework:trusted-header>
<framework:trusted-header>x-forwarded-host</framework:trusted-header>
<framework:trusted-header>x-forwarded-proto</framework:trusted-header>
<framework:trusted-header>x-forwarded-port</framework:trusted-header>
<framework:trusted-header>x-forwarded-prefix</framework:trusted-header>
<!-- or, if your proxy instead uses the "Forwarded" header -->
<framework:trusted-header>forwarded</framework:trusted-header>
</framework:config>
</container>
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// config/packages/framework.php
use Symfony\Config\FrameworkConfig;
return static function (FrameworkConfig $framework): void {
$framework
// the IP address (or range) of your proxy
->trustedProxies('192.0.0.1,10.0.0.0/8')
// trust *all* "X-Forwarded-*" headers (the ! prefix means to not trust those headers)
->trustedHeaders(['x-forwarded-for', 'x-forwarded-host', 'x-forwarded-proto', 'x-forwarded-port', 'x-forwarded-prefix'])
// or, if your proxy instead uses the "Forwarded" header
->trustedHeaders(['forwarded'])
;
};
Caution
Enabling the Request::HEADER_X_FORWARDED_HOST
option exposes the
application to HTTP Host header attacks. Make sure the proxy really
sends an x-forwarded-host
header.
The Request object has several Request::HEADER_*
constants that control exactly
which headers from your reverse proxy are trusted. The argument is a bit field,
so you can also pass your own value (e.g. 0b00110
).
Tip
You can set a TRUSTED_PROXIES
env var to configure proxies on a per-environment basis:
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# .env
TRUSTED_PROXIES=127.0.0.1,10.0.0.0/8
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# config/packages/framework.yaml
framework:
# ...
trusted_proxies: '%env(TRUSTED_PROXIES)%'
Caution
The "trusted proxies" feature does not work as expected when using the nginx realip module. Disable that module when serving Symfony applications.
But what if the IP of my Reverse Proxy Changes Constantly!
Some reverse proxies (like AWS Elastic Load Balancing) don't have a static IP address or even a range that you can target with the CIDR notation. In this case, you'll need to - very carefully - trust all proxies.
- Configure your web server(s) to not respond to traffic from any clients other than your load balancers. For AWS, this can be done with security groups.
Once you've guaranteed that traffic will only come from your trusted reverse proxies, configure Symfony to always trust incoming request:
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# config/packages/framework.yaml framework: # ... # trust *all* requests (the 'REMOTE_ADDR' string is replaced at # run time by $_SERVER['REMOTE_ADDR']) trusted_proxies: '127.0.0.1,REMOTE_ADDR'
That's it! It's critical that you prevent traffic from all non-trusted sources. If you allow outside traffic, they could "spoof" their true IP address and other information.
If you are also using a reverse proxy on top of your load balancer (e.g.
CloudFront), calling $request->server->get('REMOTE_ADDR')
won't be
enough, as it will only trust the node sitting directly above your application
(in this case your load balancer). You also need to append the IP addresses or
ranges of any additional proxy (e.g. CloudFront IP ranges) to the array of
trusted proxies.
Custom Headers When Using a Reverse Proxy
Some reverse proxies (like CloudFront with CloudFront-Forwarded-Proto
)
may force you to use a custom header. For instance you have
Custom-Forwarded-Proto
instead of X-Forwarded-Proto
.
In this case, you'll need to set the header X-Forwarded-Proto
with the value
of Custom-Forwarded-Proto
early enough in your application, i.e. before
handling the request:
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// public/index.php
// ...
$_SERVER['HTTP_X_FORWARDED_PROTO'] = $_SERVER['HTTP_CUSTOM_FORWARDED_PROTO'];
// ...
$response = $kernel->handle($request);