Config Sync architecture

This page introduces you to the architecture of Config Sync. Learning about the components created by Config Sync can give you a deeper understanding of Config Sync and might help you debug and fix issues that you encounter.

The following diagram shows the architecture of Config Sync and its related resources on a Google Kubernetes Engine (GKE) Enterprise edition cluster:

Diagram that shows the relationship between Config Sync objects and resources

In this diagram, the user creates a source of truth and installs Config Sync using the Feature Manager.

There are multiple steps to install Config Sync and each of these steps deploys additional components on your cluster:

  1. Enabling Config Sync on your cluster adds the following components:

    • The ConfigManagement Operator in a Deployment named config-management-operator.
    • The ConfigManagement custom resource definition (CRD) and object named config-management.
    • The Reconciler Manager in a Deployment named reconciler-manager.
    • The ResourceGroup Controller in a Deployment named resource-group-controller-manager.
    • The OpenTelemetry Collector in a Deployment named otel-collector.
    • Optional: The Config Sync Admission Webhook in a Deployment named admission-webhook.

    Most of these resources and objects are automatically created when installing Config Sync and you don't need to modify them.

  2. Creating RootSync and RepoSync objects adds the following components:

    • For each RootSync, a reconciler Deployment named root-reconciler-ROOTSYNC_NAME.
    • For each RepoSync, a reconciler Deployment named ns-reconciler-REPOSYNC_NAMESPACE-REPOSYNC_NAME-REPOSYNC_NAME_LENGTH.

Config Sync Deployments, Pods, and containers

The following table provides more information about the Config Sync Deployment, Pods, and containers:

Deployment name Deployment namespace Deployment description Replica count Pod name regular expression Container count Container names
config-management-operator config-management-system The ConfigManagement Operator runs on every cluster with Config Sync installed. It watches the ConfigManagement object and manages Config Sync components, like the Reconciler Manager and OpenTelemetry Collector. 1 config-management-operator-.* 1
  • manager
    		•
    reconciler-manager config-management-system The Reconciler Manager runs on every cluster with Config Sync enabled in the ConfigManagement object. It watches RootSync and RepoSync objects and manages a reconciler Deployment for each one. 1 reconciler-manager-.* 2
  • reconciler-manager
  • otel-agent
    		•
    root-reconciler config-management-system A root reconciler Deployment is created for every RootSync object. 1 root-reconciler-.* 3 - 51
  • reconciler
  • otel-agent
  • git-sync
  • helm-sync
  • oci-sync
  • gcenode-askpass-sidecar
  • hydration-controller
    		•
    ns-reconciler config-management-system A namespace reconciler Deployment is created for every RepoSync object. 1 ns-reconciler-.* 3 - 51
  • reconciler
  • otel-agent
  • git-sync
  • helm-sync
  • oci-sync
  • gcenode-askpass-sidecar
  • hydration-controller
    		•
    otel-collector config-management-monitoring The OpenTelemetry Collector runs on every cluster with Config Sync enabled in the ConfigManagement object. It collects metrics from the Config Sync components running under the config-management-system and resource-group-system namespaces, and exports these metrics to Prometheus and Cloud Monitoring. 1 otel-collector-.* 1
  • otel-collector
    		•
    resource-group-controller-manager resource-group-system The ResourceGroup Controller runs on every cluster with Config Sync enabled in the ConfigManagement object. It watches ResourceGroup objects and updates them with the current reconciliation status of each object in their inventory. A ResourceGroup object is created for every RootSync and RepoSync object to inventory the list of objects applied by the reconciler from the source of truth. 1 resource-group-controller-manager-.* 2
  • reconciler-manager
  • otel-agent
    		•
    admission-webhook config-management-system The Config Sync Admission Webhook runs on each cluster with drift prevention enabled in the ConfigManagement object. It monitors Kubernetes API requests and prevents modification or deletion of resources managed by Config Sync. The Config Sync admission webhook is disabled by default. 2 admission-webhook-.* 1
  • admission-webhook
    		•

    1 For details about when these containers are created, see Reconciler containers.

    Key components

    The following sections explore important Config Sync components in greater detail.

    ConfigManagement Operator and object

    The ConfigManagement Operator watches the ConfigManagement object and creates and manages other components needed for Config Sync to work:

    Operator actuation

    Because the ConfigManagement Operator installs some components that require cluster-admin permissions, the ConfigManagement Operator requires cluster-admin permissions as well.

    Reconciler Manager and reconcilers

    The Reconciler Manager is responsible for creating and managing the individual reconcilers that ensure your cluster configuration stays in sync.

    The Reconciler Manager creates a root reconciler for every RootSync object and a namespace reconciler for every RepoSync object. Config Sync uses this design instead of sharing a single monolithic reconciler because it improves reliability by reducing single points of failure and allows for individual reconcilers to be scaled independently.

    Root and namespace reconcilers automatically fetch configs from your source of truth and apply them to enforce the state that you want within your cluster.

    The following diagrams show how the Reconciler Manager handles controlling the lifecycle of each root reconciler and namespace reconciler:

    Diagram that shows how the Reconciler Manager controls the root reconciler Diagram that shows how the Reconciler Manager controls the namespace reconciler

    Reconciler containers

    The specific containers deployed in the reconciler Pods depend on the configuration choices you make. The following table explains more about what each of these reconciler containers do and the condition that causes Config Sync to create them:

    Container name Description Condition
    reconciler Handles syncing and drift remediation. Always enabled.
    otel-agent Receives metrics from the other reconciler containers and sends them to the OpenTelemetry Collector. Always enabled.
    git-sync Pulls configs from your Git repository to a local directory that the reconciler container can read. Enabled when spec.sourceType is git.
    helm-sync Pulls and renders Helm charts from your chart repository to a local directory that the reconciler container can read. Enabled when spec.sourceType is helm.
    oci-sync Pulls OCI images containing your configs from your container registry to a local directory that the reconciler container can read. Enabled when spec.sourceType is oci.
    gcenode-askpass-sidecar Caches Git credentials from the GKE metadata service for use by the git-sync container. Enabled when spec.sourceType is git and spec.git.auth is gcenode or gcpserviceaccount.
    hydration-controller Handles building Kustomize configurations to a local directory that the reconciler container can read. Enabled when the source includes a kustomize.yaml file.

    As shown in the preceding table, you can typically expect a container count of three to five within each reconciler Pod. The reconciler and otel-agent containers are always present. Specifying a type for your source of truth dictates which sync container is added. Additionally, the hydration-controller and gcenode-askpass-sidecar containers are created if you made the configuration changes mentioned in the table.

    ResourceGroup Controller and ResourceGroup objects

    The root and namespace reconcilers create a ResourceGroup inventory object for each RootSync and RepoSync object you set up. Each ResourceGroup object contains a list of objects synced to the cluster from the source of truth by the reconciler for that RootSync or RepoSync object. The ResourceGroup Controller then watches all the objects in the ResourceGroup object and updates the status of the ResourceGroup object with the current reconciliation status of the synced objects. This lets you check the status of the ResourceGroup object for an overview of the sync status, instead of having to query the status of every individual object yourself.

    ResourceGroup objects have the same name and namespace as their corresponding RootSync or RepoSync object. For example, for the RootSync object with the name root-sync in the namespace config-management-system, the corresponding ResourceGroup object is also named root-sync in the config-management-system namespace.

    Don't create or modify ResourceGroup objects, as this can interfere with the operation of Config Sync.

    Admission Webhook

    The Config Sync Admission Webhook is created when you enable drift prevention. Drift prevention proactively intercepts modification requests, ensuring they align with the source of truth before allowing changes.

    If you don't enable drift prevention, Config Sync still uses a self-healing mechanism to revert configuration drift. With self-healing, Config Sync continuously monitors managed objects and automatically reverses any changes that deviate from the intended state.

    RootSync and RepoSync objects

    RootSync objects configure Config Sync to create a root reconciler that watches the specified source of truth and apply objects from that source to the cluster. By default, the root reconciler for each RootSync object has cluster-admin permission. With this default permission, root reconcilers can sync both cluster-scoped and namespace-scoped resources. If needed, you can change these permissions by configuring the spec.override.roleRefs fields. RootSync objects are designed for use by cluster admins.

    RepoSync objects configure Config Sync to create a namespace reconciler that watches the specified source and apply objects from that source to a specific namespace in the cluster. Namespace reconcilers can sync any namespace-scoped resources in that namespace with custom user-specified permissions. RepoSync objects are designed for use by namespace tenants.

    How the Fleet service manages RootSync objects

    When you install Config Sync with the Google Cloud console, Google Cloud CLI, Config Connector, or Terraform, Config Sync is managed by the Fleet service, based on your inputs to the Google Cloud API.

    When your Config Sync installation is managed by the Fleet service, you can optionally also have it manage your initial RootSync object, named root-sync. This lets you bootstrap GitOps on your cluster without needing to manually apply anything to the cluster directly. If you decide not to have the Fleet service manage your initial RootSync object, you can still apply whatever RootSync and RepoSync objects you want directly to the cluster.

    The RootSync object named root-sync is created based on your inputs to the Google Cloud API, specifically the spec.configSync section of the config-management apply API. Because this API only exposes a subset of the RootSync fields, those fields are considered managed in the root-sync, while the other fields are considered unmanaged. Managed fields can only be edited using the Google Cloud API. The unmanaged fields can be edited using kubectl, or any other Kubernetes client. For an example showing you how to export the root-sync YAML, edit it locally, and re-apply it, see create and edit a RootSync configuration file.

    For manual installations, you manage Config Sync with the kubectl command-line tool or any other Kubernetes client.

    Additional RootSync and RepoSync objects

    To create additional RootSync or RepoSync objects, you can use the kubectl command-line tool or another Kubernetes client. You can also use the initial root-sync object to manage additional RootSync or RepoSync objects with GitOps, by adding their YAML manifests to the source of truth that the root-sync is configured to sync from. This method cannot be used to manage the config of the initial root-sync, because some of its fields are managed by the Fleet service. To manage the root-sync object with GitOps, use Config Connector or Terraform. To learn more about creating additional RootSync and RepoSync objects, see Configure syncing from more than one source of truth.

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