HTTP headers and Classic Load Balancers
HTTP requests and HTTP responses use header fields to send information about the HTTP
messages. Header fields are colon-separated name-value pairs that are separated by a
carriage return (CR) and a line feed (LF). A standard set of HTTP header fields is
defined in RFC 2616, Message HeadersX-Forwarded prefix. Classic Load Balancers support
the following X-Forwarded headers.
For more information about HTTP connections, see Request routing in the Elastic Load Balancing User Guide.
Prerequisites
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Confirm that your listener settings support the X-Forwarded headers. For more information, see Listener configurations for Classic Load Balancers.
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Configure your web server to log client IP addresses.
X-Forwarded headers
X-Forwarded-For
The X-Forwarded-For request header is automatically added and helps
you identify the IP address of a client when you use an HTTP or HTTPS load balancer.
Because load balancers intercept traffic between clients and servers, your server
access logs contain only the IP address of the load balancer. To see the IP address
of the client, use the X-Forwarded-For request header. Elastic Load Balancing stores the
IP address of the client in the X-Forwarded-For request header and
passes the header to your server. If the X-Forwarded-For request header
is not included in the request, the load balancer creates one with the client IP
address as the request value. Otherwise, the load balancer appends the client IP
address to the existing header and passes the header to your server. The
X-Forwarded-For request header may contain multiple IP addresses
that are comma separated. The left-most address is the client IP where the request
was first made. This is followed by any subsequent proxy identifiers, in a
chain.
The X-Forwarded-For request header takes the following form:
X-Forwarded-For: client-ip-addressThe following is an example X-Forwarded-For request header for a
client with an IP address of 203.0.113.7.
X-Forwarded-For: 203.0.113.7The following is an example X-Forwarded-For request header for a
client with an IPv6 address of
2001:DB8::21f:5bff:febf:ce22:8a2e.
X-Forwarded-For: 2001:DB8::21f:5bff:febf:ce22:8a2eX-Forwarded-Proto
The X-Forwarded-Proto request header helps you identify the protocol
(HTTP or HTTPS) that a client used to connect to your load balancer. Your server
access logs contain only the protocol used between the server and the load balancer;
they contain no information about the protocol used between the client and the load
balancer. To determine the protocol used between the client and the load balancer,
use the X-Forwarded-Proto request header. Elastic Load Balancing stores the protocol
used between the client and the load balancer in the X-Forwarded-Proto
request header and passes the header along to your server.
Your application or website can use the protocol stored in the
X-Forwarded-Proto request header to render a response that
redirects to the appropriate URL.
The X-Forwarded-Proto request header takes the following form:
X-Forwarded-Proto: originatingProtocolThe following example contains an X-Forwarded-Proto request header
for a request that originated from the client as an HTTPS request:
X-Forwarded-Proto: httpsX-Forwarded-Port
The X-Forwarded-Port request header helps you identify the
destination port that the client used to connect to the load balancer.
