open-consul/website/content/docs/connect/transparent-proxy.mdx

---
layout: docs
page_title: Connect - Transparent Proxy
sidebar_title: Transparent Proxy
description: |-
  Transparent proxy is used to direct inbound and outbound traffic to services via the Envoy proxy and configure
  upstreams via intentions.
---

# Transparent Proxy

Transparent proxy allows applications to communicate through the mesh without changing their configuration.
Transparent proxy also hardens application security by preventing direct inbound connections that bypass the mesh.

#### Without Transparent Proxy

![Diagram demonstrating that without transparent proxy, applications must "opt in" to connecting to their dependencies through the mesh](/img/consul-connect/without-transparent-proxy.png)

Without transparent proxy, application owners need to:

1. Explicitly configure upstream services, choosing a local port to access them.
1. Change application to access `localhost:<chosen port>`.
1. Configure application to listen only on the loopback interface to prevent unauthorized
   traffic from bypassing the mesh.

#### With Transparent Proxy

![Diagram demonstrating that with transparent proxy, connections are automatically routed through the mesh](/img/consul-connect/with-transparent-proxy.png)

With transparent proxy:

1. Upstreams are inferred from service intentions, so no explicit configuration
   is needed.
1. Outbound connections pointing to a KubeDNS name "just work" — network rules
   redirect them through the proxy.
1. Inbound traffic is forced to go through the proxy to prevent unauthorized
   direct access to the application.

#### Overview

Transparent proxy allows users to reach other services in the service mesh while ensuring that inbound and outbound
traffic for services in the mesh are directed through the sidecar proxy. Traffic is secured
and only reaches intended destinations since the proxy can enforce security and policy like TLS and Service Intentions.

Previously, service mesh users would need to explicitly define upstreams for a service as a local listener on the sidecar
proxy, and dial the local listener to reach the appropriate upstream. Users would also have to set intentions to allow
specific services to talk to one another. Transparent proxying reduces this duplication, by determining upstreams
implicitly from Service Intentions. Explicit upstreams are still supported in the [proxy service
registration](/docs/connect/registration/service-registration) on VMs and via the
[annotation](/docs/k8s/connect#consul-hashicorp-com-connect-service-upstreams) in Kubernetes.

To support transparent proxying, Consul's CLI now has a command
[`consul connect redirect-traffic`](/commands/connect/redirect-traffic) to redirect traffic through an inbound and
outbound listener on the sidecar. Consul also watches Service Intentions and configures the Envoy proxy with the appropriate
upstream IPs. If the default ACL policy is "allow", then Service Intentions are not required. In Consul on Kubernetes,
the traffic redirection command is automatically set up via an init container.

## Prerequisites

### Kubernetes

* To use transparent proxy on Kubernetes, Consul-helm >= `0.32.0` and Consul-k8s >= `0.26.0` are required in addition to Consul >= `1.10.0`.
* If the default policy for ACLs is "deny", then Service Intentions should be set up to allow intended services to connect to each other.
Otherwise, all Connect services can talk to all other services.
* If using Transparent Proxy, all worker nodes within a Kubernetes cluster must have the `ip_tables` kernel module running, e.g. `modprobe ip_tables`. 

The Kubernetes integration takes care of registering Kubernetes services with Consul, injecting a sidecar proxy, and
enabling traffic redirection.

## Upgrading to Transparent Proxy

~> When upgrading from older versions (i.e Consul-k8s < `0.26.0` or Consul-helm < `0.32.0`) to Consul-k8s >= `0.26.0` and Consul-helm >= `0.32.0`, please make sure to follow the upgrade steps [here](/docs/upgrading/upgrade-specific/#transparent-proxy-on-kubernetes).

## Configuration

### Enabling Transparent Proxy
Transparent proxy can be enabled in Kubernetes on the whole cluster via the Helm value:

```yaml
connectInject:
  transparentProxy:
    defaultEnabled: true
```

It can also be enabled on a per namespace basis by setting the label `consul.hashicorp.com/transparent-proxy=true` on the
Kubernetes namespace. This will override the Helm value `connectInject.transparentProxy.defaultEnabled` and define the
default behavior of Pods in the namespace. For example:
```bash
kubectl label namespaces my-app "consul.hashicorp.com/transparent-proxy=true"
```

It can also be enabled on a per service basis via the annotation `consul.hashicorp.com/transparent-proxy=true` on the
Pod for each service, which will override both the Helm value and the namespace label:

```yaml
apiVersion: v1
kind: Service
metadata:
  name: static-server
spec:
  selector:
    app: static-server
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-server
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-server
  template:
    metadata:
      name: static-server
      labels:
        app: static-server
      annotations:
        'consul.hashicorp.com/connect-inject': 'true'
        'consul.hashicorp.com/transparent-proxy': 'true'
    spec:
      containers:
        - name: static-server
          image: hashicorp/http-echo:latest
          args:
            - -text="hello world"
            - -listen=:8080
          ports:
            - containerPort: 8080
              name: http
      serviceAccountName: static-server
```

### Kubernetes HTTP Health Probes Configuration
Traffic redirection interferes with [Kubernetes HTTP health
probes](https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/) since the
probes expect that kubelet can directly reach the application container on the probe's endpoint, but that traffic will
be redirected through the sidecar proxy, causing errors because kubelet itself is not encrypting that traffic using a
mesh proxy. For this reason, Consul allows you to [overwrite Kubernetes HTTP health probes](/docs/k8s/connect/health) to point to the proxy instead.
This can be done using the Helm value `connectInject.transparentProxy.defaultOverwriteProbes`
or the Pod annotation `consul.hashicorp.com/transparent-proxy-overwrite-probes`.

### Traffic Redirection Configuration
Pods with transparent proxy enabled will have an init container injected that sets up traffic redirection for all
inbound and outbound traffic through the sidecar proxies. This will include all traffic by default, with the ability to
configure exceptions on a per-Pod basis. The following Pod annotations allow you to exclude certain traffic from redirection to the sidecar proxies:
- [`consul.hashicorp.com/transparent-proxy-exclude-inbound-ports`](/docs/k8s/connect#consul-hashicorp-com-transparent-proxy-exclude-inbound-ports)
- [`consul.hashicorp.com/transparent-proxy-exclude-outbound-ports`](/docs/k8s/connect#consul-hashicorp-com-transparent-proxy-exclude-outbound-ports)
- [`consul.hashicorp.com/transparent-proxy-exclude-outbound-cidrs`](/docs/k8s/connect#consul-hashicorp-com-transparent-proxy-exclude-outbound-cidrs)
- [`consul.hashicorp.com/transparent-proxy-exclude-uids`](/docs/k8s/connect#consul-hashicorp-com-transparent-proxy-exclude-uids)


## Known Limitations

* Traffic can only be transparently proxied when the address dialed corresponds to the address of a service in the
transparent proxy's datacenter. Services can also dial explicit upstreams in other datacenters without transparent proxy, for example, by adding an
[annotation](/docs/k8s/connect#consul-hashicorp-com-connect-service-upstreams) such as
`"consul.hashicorp.com/connect-service-upstreams": "my-service:1234:dc2"` to reach an upstream service called `my-service`
in the datacenter `dc2`.
* In the deployment configuration where a [single Consul datacenter spans multiple Kubernetes clusters](/docs/k8s/installation/deployment-configurations/single-dc-multi-k8s), services in one Kubernetes cluster must explicitly dial a service in another Kubernetes cluster using the [consul.hashicorp.com/connect-service-upstreams](/docs/k8s/connect#consul-hashicorp-com-connect-service-upstreams) annotation. An example would be
`"consul.hashicorp.com/connect-service-upstreams": "my-service:1234"`, where `my-service` is the service that exists in another Kubernetes cluster and is exposed on port `1234`. Although Transparent Proxy is enabled, KubeDNS is not utilized when communicating between services existing on separate Kubernetes clusters.
* When dialing headless services the request will be proxied using a plain TCP proxy with a 5s connection timeout.
Currently the upstream's protocol and connection timeout are not considered.

## Using Transparent Proxy

In Kubernetes, services can reach other services via their
[KubeDNS](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/) address or via Pod IPs, and that
traffic will be transparently sent through the proxy. Connect services in Kubernetes are required to have a Kubernetes
service selecting the Pods.

~> Note: In order to use KubeDNS, the Kubernetes service name will need to match the Consul service name. This will be the
case by default, unless the service Pods have the annotation `consul.hashicorp.com/connect-service` overriding the
Consul service name.

Transparent proxy is enabled by default in Consul-helm >=`0.32.0`. The Helm value used to enable/disable transparent
proxy for all applications in a Kubernetes cluster is `connectInject.transparentProxy.defaultEnabled`.

Each Pod for the service will be configured with iptables rules to direct all inbound and outbound traffic through an
inbound and outbound listener on the sidecar proxy. The proxy will be configured to know how to route traffic to the
appropriate upstream services based on [Service
Intentions](/docs/connect/config-entries/service-intentions). This means Connect services no longer
need to use the `consul.hashicorp.com/connect-service-upstreams` annotation to configure upstreams explicitly. Once the
Service Intentions are set, they can simply address the upstream services using KubeDNS.

As of Consul-k8s >= `0.26.0` and Consul-helm >= `0.32.0`, a Kubernetes service that selects application pods is required
for Connect applications, i.e:

```yaml
apiVersion: v1
kind: Service
metadata:
  name: sample-app
  namespace: default
spec:
  selector:
    app: sample-app
  ports:
    - protocol: TCP
      port: 80
```

In the example above, if another service wants to reach `sample-app` via transparent proxying,
it can dial `sample-app.default.svc.cluster.local`, using
[KubeDNS](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/).
If ACLs with default "deny" policy are enabled, it also needs a
[ServiceIntention](/docs/connect/config-entries/service-intentions) allowing it to talk to
`sample-app`.

### Headless Services
For services that are not addressed using a virtual cluster IP, the upstream service must be
configured using the [DialedDirectly](/docs/connect/config-entries/service-defaults#dialeddirectly)
option.

Individual instance addresses can then be discovered using DNS, and dialed through the transparent proxy.
When this mode is enabled on the upstream, connect certificates will be presented for mTLS and
intentions will be enforced at the destination.

Note that when dialing individual instances HTTP routing rules configured with config entries
will **not** be considered. The transparent proxy acts as a TCP proxy to the original
destination IP address.