---
layout: docs
page_title: Consul catalog v2 architecture
description: Learn about version 2 of the Consul catalog, which uses GAMMA specified resources. Learn how the v2 catalog corresponds to the v1 catalog.
---

<Warning>

The v2 catalog API and Traffic Permissions API are currently in beta. This documentation supports testing and development scenarios. Do not use these APIs in secure production environments.

</Warning>

# Consul catalog v2 architecture

This topic provides information about version 2 (v2) of the Consul catalog API. The catalog tracks registered services and their locations for both service discovery and service mesh use cases.

Consul supports the v2 catalog for service mesh use cases on Kubernetes deployments only. For more information about Consul’s default catalog, refer to [v1 Catalog API](/consul/docs/architecture/catalog).

## Introduction

When Consul registers services, it records [user-defined and Consul-assigned information](/consul/docs/architecture/catalog#catalog-structure). To determine a service’s identity, v1 of the catalog API records the following information:

- IDs of the specific _service instances_ that are registered
- Locations of the _nodes_ the instances run on
- Names of the _services_ the instances are associated with

This information enables Consul to associate service names with the individual instances and their unique network addresses, which makes it essential to Consul’s service discovery and service mesh operations.

The [Consul v1 catalog API](/consul/docs/architecture/catalog) was designed prior to the introduction of Consul’s service mesh features. One major implication of this design is that communication in Consul’s service mesh is secured through Consul's ACL system, which requires that a Kubernetes ServiceAccount resource match the Service name. As a result, only one Kubernetes Service can represent a service instance in the v1 catalog.

The v2 catalog API aligns more closely with the [Kubernetes Gateway API's GAMMA initiative](https://gateway-api.sigs.k8s.io/concepts/gamma/), which conceptualizes a Kubernetes Service as having two facets:

- The Service _front end_ is a combination of cluster IP and DNS name
- The Service _back end_ is a collection of endpoint IPs

For more information about the differences between the two facets and their impact on how Kubernetes directs requests, refer to [The Different Facets of a Service](https://gateway-api.sigs.k8s.io/concepts/service-facets/) in the Kubernetes documentation.

Consul's v2 catalog API makes a similar distinction, enabling it associate Kubernetes Pods with multiple Kubernetes Services. As a direct result of this change in catalog structure, Consul can register Services and Pods with multiple ports. For more information about how the differences between the catalog API impacts other Consul operations, refer to [changes to Consul's existing architecture](#changes-to-consul-s-existing-architecture).

The v2 catalog API is available alongside the existing v1 catalog API, but the catalogs cannot be used simultaneously. The v2 catalog is disabled by default. This beta release is for testing and development purposes only. We do not recommend implementing v2 in production environments or migrating to v2 until the API is generally available.

## Catalog structure

Consul v1.17 introduces a new version of the catalog API designed to bridge differences between the Consul and Kubernetes data models. The v2 catalog API continues to track services and nodes for Consul, but it replaces service instances with _workloads_ and _workload identites_.

### Catalog resources

The following table describes resources in the v2 catalog, how they generally compare to the v1 catalog and Kubernetes resources, and whether they are created by Kubernetes or computed by Consul when it registers a service.

| Catalog v2 resource | Resource group | Description | Catalog v1 analogue | Kubernetes analogue | Source |
| :------------------ | :------------- | :---------- | :--------------------------- | :--------------------------- | :----- |
| Service             | `catalog`      | The name of the service Consul registers a workload under. | Service | [Kubernetes Service](https://kubernetes.io/docs/concepts/services-networking/service/)  | Created by Kubernetes |
| Node | `catalog`      | The address of the Consul node where the workload runs. | Node | [Kubernetes Node](https://kubernetes.io/docs/concepts/architecture/nodes/) | Computed by Consul |
| Workload | `catalog`      | An application instance running in a set of one or more Pods scheduled according to a Kubernetes Workload resource such as a Deployment or StatefulSet. | Service instance | [Kubernetes Pod](https://kubernetes.io/docs/concepts/workloads/pods/) | Created by Kubernetes |
| Workload identity | `auth`      | Provides a distinct identity for a workload to assume. Each workload identity is tied to an Envoy proxy. This identity is used when Consul generates mTLS certificates. | Service name | [Kubernetes Service Accounts](https://kubernetes.io/docs/concepts/security/service-accounts/) | Created by Kubernetes |
| Service endpoint | Maps services to workload addresses and endpoints. | None  | [Kubernetes Endpoints](https://kubernetes.io/docs/reference/kubernetes-api/service-resources/endpoints-v1/) | Computed by Consul |
| Health status | `catalog`      | A resource for reporting the health status of a workload. | Service instance health status | [PodStatus](https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#PodStatus) | Created by Kubernetes |
| Health check | None | A resource for defining the health checks for a workload. | [Service instance health check](/consul/docs/services/usage/checks) | [Liveness, Readiness, and Startup Probes](https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#container-probes) | Created by Kubernetes |
| Proxy configuration | `mesh` | Represents a configuration for a sidecar or gateway proxy. | `Proxy` field in service definition | None | Created by Kubernetes or user CRD |
| Destinations | `catalog`      | Represents explicit service upstreams. When using the v1 catalog, these upstreams are configured in Helm chart as [Upstream Service annotations](/consul/docs/k8s/annotations-and-labels#consul-hashicorp-com-connect-service-upstreams) | [Proxy Configuration](/consul/docs/connect/proxies/envoy#envoy-proxy-configuration-for-service-mesh) | None | Created by Kubernetes |
| Traffic permissions| `auth`      | Enables L4 traffic authorization according to workload identity instead of service identity. | [Service intentions](/consul/docs/connect/intentions) | None | Created by user CRD |
