Configuring Gateway Network Topology
Forwarding external client attributes (IP address, certificate info) to destination workloads
Many applications require knowing the client IP address and certificate information of the originating request to behave
properly. Notable cases include logging and audit tools that require the client IP be populated and security tools,
such as Web Application Firewalls (WAF), that need this information to apply rule sets properly. The ability to
provide client attributes to services has long been a staple of reverse proxies. To forward these client
attributes to destination workloads, proxies use the X-Forwarded-For
(XFF) and X-Forwarded-Client-Cert
(XFCC) headers.
Today’s networks vary widely in nature, but support for these attributes is a requirement no matter what the network topology is. This information should be preserved and forwarded whether the network uses cloud-based Load Balancers, on-premise Load Balancers, gateways that are exposed directly to the internet, gateways that serve many intermediate proxies, and other deployment topologies not specified.
While Istio provides an ingress gateway, given the varieties of architectures mentioned above, reasonable defaults are not able to be shipped that support the proper forwarding of client attributes to the destination workloads. This becomes ever more vital as Istio multicluster deployment models become more common.
For more information on X-Forwarded-For
, see the IETF’s RFC.
Configuring network topologies
Configuration of XFF and XFCC headers can be set globally for all gateway workloads via MeshConfig
or per gateway using
a pod annotation. For example, to configure globally during install or upgrade when using an IstioOperator
custom resource:
spec:
meshConfig:
defaultConfig:
gatewayTopology:
numTrustedProxies: <VALUE>
forwardClientCertDetails: <ENUM_VALUE>
You can also configure both of these settings by adding the proxy.istio.io/config
annotation to the Pod spec
of your Istio ingress gateway.
...
metadata:
annotations:
"proxy.istio.io/config": '{"gatewayTopology" : { "numTrustedProxies": <VALUE>, "forwardClientCertDetails": <ENUM_VALUE> } }'
Configuring X-Forwarded-For Headers
Applications rely on reverse proxies to forward client attributes in a request, such as X-Forward-For
header. However, due to the variety of network
topologies that Istio can be deployed in, you must set the numTrustedProxies
to the number of trusted proxies deployed in front
of the Istio gateway proxy, so that the client address can be extracted correctly.
This controls the value populated by the ingress gateway in the X-Envoy-External-Address
header
which can be reliably used by the upstream services to access client’s original IP address.
For example, if you have a cloud based Load Balancer and a reverse proxy in front of your Istio gateway, set numTrustedProxies
to 2
.
Example using X-Forwarded-For capability with httpbin
Run the following command to create a file named
topology.yaml
withnumTrustedProxies
set to2
and install Istio:$ cat <<EOF > topology.yaml apiVersion: install.istio.io/v1alpha1 kind: IstioOperator spec: meshConfig: defaultConfig: gatewayTopology: numTrustedProxies: 2 EOF $ istioctl install -f topology.yaml
Create an
httpbin
namespace:$ kubectl create namespace httpbin namespace/httpbin created
Set the
istio-injection
label toenabled
for sidecar injection:$ kubectl label --overwrite namespace httpbin istio-injection=enabled namespace/httpbin labeled
Deploy
httpbin
in thehttpbin
namespace:$ kubectl apply -n httpbin -f @samples/httpbin/httpbin.yaml@
Deploy a gateway associated with
httpbin
:
$ kubectl apply -n httpbin -f @samples/httpbin/httpbin-gateway.yaml@
$ kubectl apply -n httpbin -f @samples/httpbin/gateway-api/httpbin-gateway.yaml@
$ kubectl wait --for=condition=programmed gtw -n httpbin httpbin-gateway
- Set a local
GATEWAY_URL
environmental variable based on your Istio ingress gateway’s IP address:
$ export GATEWAY_URL=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.status.loadBalancer.ingress[0].ip}')
$ export GATEWAY_URL=$(kubectl get gateways.gateway.networking.k8s.io httpbin-gateway -n httpbin -ojsonpath='{.status.addresses[0].value}')
Run the following
curl
command to simulate a request with proxy addresses in theX-Forwarded-For
header:$ curl -s -H 'X-Forwarded-For: 56.5.6.7, 72.9.5.6, 98.1.2.3' "$GATEWAY_URL/get?show_env=true" { "args": { "show_env": "true" }, "headers": { "Accept": ... "Host": ... "User-Agent": ... "X-Envoy-Attempt-Count": ... "X-Envoy-External-Address": "72.9.5.6", "X-Forwarded-Client-Cert": ... "X-Forwarded-For": "56.5.6.7, 72.9.5.6, 98.1.2.3,10.244.0.1", "X-Forwarded-Proto": ... "X-Request-Id": ... }, "origin": "56.5.6.7, 72.9.5.6, 98.1.2.3,10.244.0.1", "url": ... }
The above output shows the request headers that the httpbin
workload received. When the Istio gateway received this
request, it set the X-Envoy-External-Address
header to the second to last (numTrustedProxies: 2
) address in the
X-Forwarded-For
header from your curl command. Additionally, the gateway appends its own IP to the X-Forwarded-For
header before forwarding it to the httpbin workload.
Configuring X-Forwarded-Client-Cert Headers
From Envoy’s documentation regarding XFCC:
To configure how XFCC headers are handled, set forwardClientCertDetails
in your IstioOperator
apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
spec:
meshConfig:
defaultConfig:
gatewayTopology:
forwardClientCertDetails: <ENUM_VALUE>
where ENUM_VALUE
can be of the following type.
ENUM_VALUE | |
---|---|
UNDEFINED | Field is not set. |
SANITIZE | Do not send the XFCC header to the next hop. |
FORWARD_ONLY | When the client connection is mTLS (Mutual TLS), forward the XFCC header in the request. |
APPEND_FORWARD | When the client connection is mTLS, append the client certificate information to the request’s XFCC header and forward it. |
SANITIZE_SET | When the client connection is mTLS, reset the XFCC header with the client certificate information and send it to the next hop. This is the default value for a gateway. |
ALWAYS_FORWARD_ONLY | Always forward the XFCC header in the request, regardless of whether the client connection is mTLS. |
See the Envoy documentation for examples of using this capability.
PROXY Protocol
The PROXY protocol allows for exchanging and preservation of client attributes between TCP proxies,
without relying on L7 protocols such as HTTP and the X-Forwarded-For
and X-Envoy-External-Address
headers. It is intended for scenarios where an external TCP load balancer needs to proxy TCP traffic through an Istio gateway to a backend TCP service and still expose client attributes such as source IP to upstream TCP service endpoints. PROXY protocol can be enabled via EnvoyFilter
.
If your external TCP load balancer is configured to forward TCP traffic and use the PROXY protocol, the Istio Gateway TCP listener must also be configured to accept the PROXY protocol.
To enable PROXY protocol on all TCP listeners on the gateways, set proxyProtocol
in your IstioOperator
. For example:
apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
spec:
meshConfig:
defaultConfig:
gatewayTopology:
proxyProtocol: {}
Alternatively, deploy a gateway with the following pod annotation:
metadata:
annotations:
"proxy.istio.io/config": '{"gatewayTopology" : { "proxyProtocol": {} }}'
The client IP is retrieved from the PROXY protocol by the gateway and set (or appended) in the X-Forwarded-For
and X-Envoy-External-Address
header. Note that the PROXY protocol is mutually exclusive with L7 headers like X-Forwarded-For
and X-Envoy-External-Address
. When PROXY protocol is used in conjunction with the gatewayTopology
configuration, the numTrustedProxies
and the received X-Forwarded-For
header takes precedence in determining the trusted client addresses, and PROXY protocol client information will be ignored.
Note that the above example only configures the Gateway to accept incoming PROXY protocol TCP traffic - See the Envoy documentation for examples of how to configure Envoy itself to communicate with upstream services using PROXY protocol.