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docs: Consul DNS views on Kubernetes (#21802)

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1.21.0-dev

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Use a k8s ConfigMap to configure KubeDNS or CoreDNS so that you can use Consul's `<service-name>.service.consul` syntax for queries and other DNS requests. In Kubernetes, this process uses either stub-domain or proxy configuration.
---
# Resolve Consul DNS Requests in Kubernetes
# Resolve Consul DNS requests in Kubernetes
One of the primary query interfaces to Consul is the
[DNS interface](/consul/docs/services/discovery/dns-overview). You can configure Consul DNS in
This topic describes how to configure Consul DNS in
Kubernetes using a
[stub-domain configuration](https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/#configure-stub-domain-and-upstream-dns-servers)
if using KubeDNS or a [proxy configuration](https://coredns.io/plugins/forward/) if using CoreDNS.
Once configured, DNS requests in the form `<consul-service-name>.service.consul` will
resolve for services in Consul. This will work from all Kubernetes namespaces.
resolve for services in Consul. This works from all Kubernetes namespaces.
-> **Note:** If you want requests to just `<consul-service-name>` (without the `.service.consul`) to resolve, then you'll need
to turn on [Consul to Kubernetes Service Sync](/consul/docs/k8s/service-sync#consul-to-kubernetes).

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---
layout: docs
page_title: Enable Consul DNS proxy for Kubernetes
description: ->
Learn how to schedule a Consul DNS proxy for a Kubernetes Pod so that your services can return Consul DNS results for service discovery.
---
# Enable Consul DNS proxy for Kubernetes
This page describes the process to deploy a Consul DNS proxy in a Kubernetes Pod so that Services can resolve Consul DNS requests. For more information, refer to [Consul DNS views for Kubernetes](/consul/docs/k8s/dns/views).
## Prerequisites
You must meet the following minimum application versions to enable the Consul DNS proxy for Kubernetes:
- Consul v1.20.0 or higher
- Either Consul on Kubernetes or the Consul Helm chart, v1.6.0 or higher
## Update Helm values
To enable the Consul DNS proxy, add the required [Helm values](/consul/docs/k8s/helm) to your Consul on Kubernetes deployment.
```yaml
connectInject:
enabled: true
dns:
enabled: true
proxy: true
```
### ACLs
We recommend you create a dedicated [ACL token with DNS permissions](/consul/docs/security/acl/tokens/create/create-a-dns-token) for the Consul DNS proxy. The Consul DNS proxy requires these ACL permissions.
```hcl
node_prefix "" {
policy = "read"
}
service_prefix "" {
policy = "read"
}
```
You can manage ACL tokens with Consul on Kubernetes, or you can configure the DNS proxy to access a token stored in Kubernetes secret. To use a Kubernetes secret, add the following configuration to your Helm chart.
```yaml
dns:
proxy:
aclToken:
secretName: <Consul-DNS-Token>
secretKey: <Token-Value>
```
## Retrieve Consul DNS proxy's address
To look up the IP address for the Consul DNS proxy in the Kubernetes Pod, run the following command.
```shell-session
$ kubectl get services –-all-namespaces --selector="app=consul,component=dns-proxy" --output jsonpath='{.spec.clusterIP}'
10.96.148.46
```
Use this address when you update the ConfigMap resource.
## Update Kubernetes ConfigMap
Create or update a [ConfigMap object in the Kubernetes cluster](https://kubernetes.io/docs/concepts/configuration/configmap/) so that Kubernetes forwards DNS requests with the `.consul` domain to the IP address of the Consul DNS proxy.
The following example of a `coredns-custom` ConfigMap configures Kubernetes to forward Consul DNS requests in the cluster to the Consul DNS Proxy running on `10.96.148.46`. This resource modifies the CoreDNS without modifications to the original `Corefile`.
```yaml
kind: ConfigMap
metadata:
name: coredns-custom
namespace: kube-system
data:
consul.server: |
consul:53 {
errors
cache 30
forward . 10.96.148.46
reload
}
```
After updating the DNS configuration, perform a rolling restart of the CoreDNS.
```shell-session
kubectl -n kube-system rollout restart deployment coredns
```
For more information about using a `coredns-custom` resource, refer to the [Rewrite DNS guide in the Azure documentation](https://learn.microsoft.com/en-us/azure/aks/coredns-custom#rewrite-dns). For general information about modifying a ConfigMap, refer to [the Kubernetes documentation](https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/#coredns).
## Next steps
After you enable the Consul DNS proxy, services in the Kubernetes cluster can resolve Consul DNS addresses.
- To learn more about Consul DNS for service discovery, refer to [DNS usage overview](/consul/docs/services/discovery/dns-overview).
- If your datacenter has ACLs enabled, create a [Consul ACL token](/consul/docs/security/acl/tokens) for the Consul DNS proxy and then restart the DNS proxy.
- To enable service discovery across admin partitions, [export services between partitions](/consul/docs/connect/config-entries/exported-services).
- To use Consul DNS for service discovery with other runtimes, across cloud regions, or between cloud providers, [establish a cluster peering connection](/consul/docs/k8s/connect/cluster-peering/usage/establish-peering).

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---
layout: docs
page_title: Consul DNS views for Kubernetes
description: ->
Kubernetes clusters can use the Consul DNS proxy to return service discovery results from the Consul catalog. Learn about how to configure your k8s cluster so that applications can resolve Consul DNS addresses without gossip communication.
---
# Consul DNS views for Kubernetes
This topic describes how to schedule a dedicated Consul DNS proxy in a Kubernetes Pod so that applications in Kubernetes can resolve Consul DNS addresses. You can use the Consul DNS proxy to enable service discovery across admin partitions in Kubernetes deployments without needing to deploy Consul client agents.
## Introduction
Kubernetes operators typically choose networking tools such as [kube-dns](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/) or [CoreDNS](https://kubernetes.io/docs/tasks/administer-cluster/coredns/) for their service discovery operations, and choose to bypass Consul DNS entirely. These DNS options are often sufficient for service networking operations within a single Kubernetes cluster.
Consul on Kubernetes supports [configuring Kubernetes to resolve Consul DNS](/consul/docs/k8s/dns). However, two common challenges result when you rely on these configurations:
- Kubernetes requires Consul to use gossip communication with agents or dataplanes in order to enable Consul DNS.
- Consul requires that admin partitions be included in the DNS address. Otherwise, DNS queries assume the `default` partition by default.
The `consul-dns` proxy does not require the presence of Consul client agents or Consul dataplanes, removing gossip communication as a requirement for Consul DNS on Kubernetes. The proxy is also designed for deployment in a Kubernetes cluster with [external servers enabled](/consul/docs/k8s/deployment-configurations/servers-outside-kubernetes). When a cluster runs in a non-default admin partition and uses the proxy to query external servers, Consul automatically recognizes the admin partition that originated the request and returns service discovery results scoped to that specific admin partition.
To use Consul DNS for service discovery on Kubernetes, deploy a `dns-proxy` service in each Kubernetes Pod that needs to resolve Consul DNS. Kubernetes sends all DNS requests to the Kubernetes controller first. The controller forwards requests for the `.consul` domain to the `dns-proxy` service, which then queries the Consul catalog and returns service discovery results.
## Workflows
The process to enable Consul DNS views for service discovery in Kubernetes deployments consists of the following steps:
1. In a cluster configured to use [external Consul servers](/consul/docs/k8s/deployment-configurations/servers-outside-kubernetes), update the Helm values for your Consul on Kubernetes deployment so that `dns.proxy.enabled=true`. When you apply the updated configuration, Kubernetes deploys the Consul DNS proxy.
1. Look up the IP address for the Consul DNS proxy in the Kubernetes cluster.
1. Update the ConfigMap resource in the Kubernetes cluster so that it forwards requests for the `.consul` domain to the IP address of the Consul DNS proxy.
For more information about the underlying concepts described in this workflow, refer to [DNS forwarding overview](/consul/docs/services/discovery/dns-forwarding).
## Benefits
Consul on Kubernetes currently uses [Consul dataplanes](/consul/docs/connect/dataplane) by default. These lightweight processes provide Consul access to the sidecar proxies in the service mesh, but leave Kubernetes in charge of most other service discovery and service mesh operations.
- **Use Kubernetes DNS and Consul DNS in a single deployment**. The Consul DNS proxy enables any application in a Pod to resolve an address through Consul DNS without disrupting the underlying Kubernetes DNS functionality.
- **Consul service discovery using fewer resources**. When you use the Consul DNS proxy for service discovery, you do not need to schedule Consul client agents or dataplanes as sidecars. One Kubernetes Service that uses the same resources as a single Consul dataplane provides Pods access to the Consul service catalog.
- **Consul DNS without gossip communication**. The Consul DNS service runs on both Consul server and Consul client agents, which use [gossip communication](/consul/docs/security/encryption/gossip) to ensure that service discovery results are up-to-date. The Consul DNS proxy provides access to Consul DNS without the security overhead of agent-to-agent gossip.
## Constraints and limitations
If you experience issues using the Consul DNS proxy for Kubernetes, refer to the following list of technical constraints and limitations.
- You must use Kubernetes as your runtime to use the Consul DNS proxy. You cannot schedule the Consul DNS proxy in other container-based environments.
- To perform DNS lookups on other admin partitions, you must [export services between partitions](/consul/docs/connect/config-entries/exported-services) before you can query them.

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---
layout: docs
page_title: Enable dynamic DNS queries
page_title: Scale Consul DNS
description: ->
You tune Consul DNS query handling to balance between current information and reducing request response time. Learn how to enable caching by modifying TTL values, how to return stale results from the DNS cache, and how to configure Consul for negative response caching.
---
# DNS caching
# Scale Consul DNS
This page describes the process to return cached results in response to DNS lookups. Consul agents can use DNS caching to reduce response time, but might provide stale information in the process.
## Introduction
## Scaling techniques
By default, Consul serves all DNS results with a `0` TTL value, which prevents any
caching. This configuration returns the most recent information because each DNS lookup
runs every time. However, this configuration adds latency to each lookup and can potentially
exhaust the query throughput of a datacenter.
By default, Consul serves all DNS results with a `0` TTL value so that it returns the most recent information. When operating at scale, this configuration may result in additional latency because servers must respond to every DNS query. There are several strategies for distributing this burden in your datacenter:
There are several ways you can modify to fine-tune Consul DNS lookup behavior to best suit your network's requirements.
- [Allow Stale Reads](#stale-reads). Allows other servers besides the leader to answer the query rather than forwarding it to the leader.
- [Configure DNS TTLs](#ttl-values). Configure DNS time-to-live (TTL) values for nodes or services so that the DNS subsystem on the container’s operating system can cache responses. Services then resolve DNS queries locally without any external requests.
- [Add Read Replicas](/consul/docs/enterprise/read-scale). Enterprise users can use read replicas, which are additional Consul servers that replicate cluster data without participating in the Raft quorum.
- [Use Cache to prevent server requests](/consul/docs/agent/config/config-files#dns_use_cache). Configure the Consul client to use its agent cache to subscribe to events about a service or node. After you establish the watch, the local Consul client agent can resolve DNS queries about the service or node without querying Consul servers.
The following table describes the availability of each scaling technique depending on whether you configure Consul to offload DNS requests from the cluster leader to a client agent, dataplane, or DNS proxy.
| Scaling technique | Supported by client agents | Supported by dataplanes | Supported by Consul DNS Proxy |
| :---------------------------------- | :---------------------------: | :---------------------------: | :---------------------------: |
| Configure DNS TTLs | &#9989; | &#9989; | &#9989; |
| Allow Stale Reads | &#9989; | &#9989; | &#9989; |
| Add Read Replicas | &#9989; | &#9989; | &#9989; |
| Use Cache to prevent server request | &#9989; | &#10060; | &#10060; |
For more information about considerations for Consul deployments that operate at scale, refer to [Operating Consul at Scale](/consul/docs/architecture/scale).
## TTL values ((#ttl))

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@ -20,12 +20,13 @@ When configured with default values, Consul exposes the DNS interface on port `8
Instead of running Consul with an administrative or root account, you can forward appropriate queries to Consul, running on an unprivileged port, from another DNS server or using port redirect.
There are two configurations for a node's DNS forwarding behavior:
- **Conditional DNS forwarding**: the local DNS servers are configured to forward to Consul only queries relative to the `.consul` zone. All other queries are still served via the default DNS server in the node.
- **Full DNS forwarding**: Consul serves all DNS queries and forwards to a remote DNS server the ones outside `.consul` domain.
### Conditional DNS forwarding
We recommend the conditional DNS forwarding approach. This configuration lowers the Consul agent's resource consumption by limiting the number of DNS requests it handles.
We recommend the conditional DNS forwarding approach. This configuration lowers the Consul agent's resource consumption by limiting the number of DNS requests it handles.
![Consul DNS conditional forwarding - Only .consul requests are routed to Consul](/img/consul-dns-conditional-forwarding.png#light-theme-only)
![Consul DNS conditional forwarding - Only .consul requests are routed to Consul](/img/consul-dns-conditional-forwarding-dark.png#dark-theme-only)
@ -43,7 +44,7 @@ This approach can be useful in scenarios where the Consul agent's node is alloca
This behavior is not enabled by default. Consul standard configuration only resolves DNS records inside the `.consul` zone. To enable DNS forwarding, you need to set the [recursors](/consul/docs/agent/config/config-files#recursors) option in your Consul configuration.
In this scenario, if a Consul DNS reply includes a `CNAME` record pointing outside the `.consul` top level domain, then the DNS reply only includes `CNAME` records by default.
In this scenario, if a Consul DNS reply includes a `CNAME` record pointing outside the `.consul` top level domain, then the DNS reply only includes `CNAME` records by default.
When `recursors` is set and the upstream resolver is functioning correctly, Consul tries to resolve CNAMEs and include any records (for example, A, AAAA, PTR) for them in its DNS reply. In these scenarios, Consul is used for full DNS forwarding and is able to serve queries for all domains.

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This topic provides overview information about how to look up Consul nodes and services using the Consul DNS.
## Consul DNS
The Consul DNS is the primary interface for discovering services registered in the Consul catalog. The DNS enables you to look up services and nodes registered with Consul using terminal commands instead of making HTTP API requests to Consul.
We recommend using the DNS for service discovery in virtual machine (VM) environments because it removes the need to modify native applications so that they can consume the Consul service discovery APIs.
@ -17,19 +18,29 @@ We recommend using the DNS for service discovery in virtual machine (VM) environ
The DNS has several default configurations, but you can customize how the server processes lookups. Refer to [Configure DNS Behaviors](/consul/docs/services/discovery/dns-configuration) for additional information.
### DNS versus native app integration
You can use DNS to reach services registered with Consul or modify your application to natively consume the Consul service discovery HTTP APIs.
We recommend using the DNS because it is less invasive. You do not have to modify your application with Consul to retrieve the service’s connection information. Instead, you can use a DNS fully qualified domain (FQDN) that conforms to Consul's lookup format to retrieve the relevant information.
Refer to [ Native App Integration](/consul/docs/connect/native) and its [Go package](/consul/docs/connect/native/go) for additional information.
Refer to [Native App Integration](/consul/docs/connect/native) and its [Go package](/consul/docs/connect/native/go) for additional information.
### DNS versus upstreams
If you are using Consul for service discovery and have not enabled service mesh features, then use the DNS to discover services and nodes in the Consul catalog.
If you are using Consul for service mesh on VMs, you can use upstreams or DNS. We recommend using upstreams because you can query services and nodes without modifying the application code or environment variables. Refer to [Upstream Configuration Reference](/consul/docs/connect/proxies/proxy-config-reference#upstream-configuration-reference) for additional information.
If you are using Consul on Kubernetes, refer to [the upstreams annotation documentation](/consul/docs/k8s/annotations-and-labels#consul-hashicorp-com-connect-service-upstreams) for additional information.
## Consul DNS on Kubernetes
Consul on Kubernetes supports approaches to using the Consul DNS in Kubernetes clusters.
For service discovery operations, refer to [Consul DNS views on Kubernetes](/consul/docs/k8s/dns/views).
For service mesh operations, refer to [Resolve Consul DNS requests in Kubernetes](/consul/docs/k8s/dns/enable).
## DNS forwarding
You can configure your local DNS servers to use Consul.
@ -37,6 +48,7 @@ You can configure your local DNS servers to use Consul.
Refer to [DNS Forwarding](/consul/docs/services/discovery/dns-forwarding) for additional information.
## Static queries
Node lookups and service lookups are the fundamental types of static queries. Depending on your use case, you may need to use different query methods and syntaxes to query the DNS for services and nodes.
Consul relies on a very specific format for queries to resolve names. Note that all queries are case-sensitive.
@ -44,4 +56,5 @@ Consul relies on a very specific format for queries to resolve names. Note that
Refer to [Perform Static DNS Lookups](/consul/docs/services/discovery/dns-static-lookups) for details about how to perform node and service lookups.
## Prepared queries
Prepared queries are configurations that enable you to register complex DNS queries. They provide lookup features that extend Consul's service discovery capabilities, such as filtering by multiple tags and automatically querying remote datacenters for services if no healthy nodes are available in the local datacenter. You can also create prepared query templates that match names using a prefix match, allowing a single template to apply to potentially many services. Refer to [Enable Dynamic DNS Queries](/consul/docs/services/discovery/dns-dynamic-lookups) for additional information.

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@ -1675,7 +1675,25 @@
},
{
"title": "Consul DNS",
"path": "k8s/dns"
"routes": [
{
"title": "DNS proxy for service discovery",
"routes": [
{
"title": "Overview",
"path": "k8s/dns/views"
},
{
"title": "Enable Consul DNS proxy",
"path": "k8s/dns/views/enable"
}
]
},
{
"title": "Enable on dataplanes",
"path": "k8s/dns/enable"
}
]
},
{
"title": "Upgrade",

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@ -247,4 +247,14 @@ module.exports = [
destination: '/consul/docs/architecture/catalog#v2-catalog',
permanent: true,
},
{
source: '/consul/docs/k8s/dns',
destination: '/consul/docs/k8s/dns/enable',
permanent: true,
},
{
source: '/consul/docs/:version(v1\.(?:11|12|13|14|15|16|17|18)\.x)/k8s/dns/enable',
destination: '/consul/docs/:version/k8s/dns',
permanent: true,
}
]

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