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ADR001: Facilitate Centralized Instance

  • Status: accepted
  • Date: 2022-04-11

Context and Problem Statement

Today, kobs has a built-in multi cluster support, but this requires to expose data sources like Prometheus or Elasticsearch to the internet if the central kobs instance is running in another network.

This comes with a lot of necessary configuration and security concerns.

Decision Drivers

If there is a multi-cluster setup (e.g. to implement multi-tenancy) and e.g. for security reasons it is not possible to expose the data sources one have to run a kobs instance for every Kubernetes cluster. As a result, there is no one place to centrally access observability data.

Considered Options

  • Central instance access data from other Kubernetes clusters via KubeAPI
  • Rework architecture and introduce an in-cluster component

Decision Outcome

Chosen option: "Rework Architecture", because expose KubeAPI and provide a .kubeconfig comes with security concerns.

This ADR describes the architectural changes necessary to enable a centralized kobs instance that can access data from multiple environments without having to expose the various data sources.

Decision Details

Rework the architecture and introduce new components:

  • kobs Hub
  • kobs Satellite

The communication between Hub and Satellite is HTTP based.

graph LR
    usr((User)) --> hub(Hub)
    hub --> sat1(Satellite)
    hub --> sat2(Satellite)
    hub --> sat3(...)
    sat1 --> p11(Plugin)
    sat1 --> p12(Plugin)
    sat2 --> p21(Plugin)
    sat2 --> p22(...)

kobs Satellite

  • A Satellite is running in every Kubernetes cluster and knows how to communicate with the data sources for the particular plugins.
  • The Satellite gets called by Hub
  • A Satellite can be utilized by multiple Hubs

kobs Hub

  • The Hub knows about Satellites
  • kobs Hub is the central component which aggregates the data from Satellites and make it accessible via a UI.
  • For performance and resilience reasons a cache is added to the Hub


Let's briefly describe the options which can be used for configuring the hub to satellite communication.

Option 1: Satellite Self-Registration

  • A Satellite got a configuration where the Hub is running
  • Satellite performs a register call on start-up
  • Satellite send heart-beat to Hub

Pros: - Less configuration on Hub - Suitable for many Satellites

Cons: - Unclear how to implement un-register when a Satellite is no-longer running (e.g. a cluster was deleted)

Option 2: Static Hub Configuration

  • List of known Satellites is a static Hub configuration

Pros: - No un-/register logic needs to be implemented - No configuration on Satellite

Cons: - Configuration list of Satellites might become large in setups with a lot of clusters - Adding Satellites remains a manual task


Option 2 ("static Hub configuration") is chosen, because of less complexity and currently no setups with large number of clusters is known.

Positive Consequences

  • It will facilitate the development of new plugins for integration with other services.

Negative Consequences

  • This will require subsequent rework for kobs Application