// It is provided as a write-only input field for convenience.
  // All keys and values are merged into the data field on write, overwriting any existing values.
  // The stringData field is never output when reading from the API.
  // +k8s:conversion-gen=false
  // +optional
  map<string, string> stringData = 4;

  // Used to facilitate programmatic handling of secret data.

# Controllers

Istio has a variety of [controllers](https://kubernetes.io/docs/concepts/architecture/controller/), which basically watch some inputs and do something.
This can be reading from Kubernetes and writing other objects back, writing to proxies over XDS, etc.

Unfortunately, writing controllers is very error prone, even for seemingly simple cases.
To work around this, Istio has a variety of abstractions meant to make writing controllers easier.

## Clients

```mermaid
graph TD
    subgraph ConfigStore
        xcs(XDS Client)
        ccs(CRD Client)
        fcs(Filesystem Client)
        acs(Aggregate)

  // singularResource is the singular name of the resource.  This allows clients to handle plural and singular opaquely.
  // For many clients the singular form of the resource will be more understandable to users reading messages and should be used when integrating the name of the resource into a sentence.
  // The command line tool kubectl, for example, allows use of the singular resource name in place of plurals.