Document spintainer

Signed-off-by: Caleb Schoepp <[email protected]>

Author: calebschoepp

content/en/docs/misc/spintainer-executor.md

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+---
+title: Spintainer Executor
+description: An overview of what the Spintainer Executor does and how it can be used.
+categories: [SpinKube]
+tags: []
+---
+
+# The Spintainer Executor
+
+The Spintainer (a play on the words Spin and container) executor is a [SpinAppExecutor](../../reference/spin-app-executor) that runs Spin applications directly in a container rather than via the [shim](../../topics/architecture#containerd-shim-spin). This is useful for a number of reasons:
+
+- Provides the flexibility to:
+  - Use any Spin version you want.
+  - Use any custom triggers or plugins you want.
+- Allows you to use SpinKube even if you don't have the cluster permissions to install the shim.
+
+> Note: We recommend using the shim for most use cases. The spintainer executor is best saved as a workaround.
+
+## How to create a spintainer executor
+
+The following is some sample configuration for a spintainer executor:
+
+```yaml
+apiVersion: core.spinkube.dev/v1alpha1
+kind: SpinAppExecutor
+metadata:
+  name: spintainer
+spec:
+  createDeployment: true
+  deploymentConfig:
+    installDefaultCACerts: true
+    spinImage: ghcr.io/fermyon/spin:v2.7.0
+```
+
+Save this into a file named `spintainer-executor.yaml` and then apply it to the cluster.
+
+```bash
+kubectl apply -f spintainer-executor.yaml
+```
+
+## How to use a spintainer executor
+
+To use the spintainer executor you must reference it as the executor of your `SpinApp`.
+
+```yaml
+apiVersion: core.spinkube.dev/v1alpha1
+kind: SpinApp
+metadata:
+  name: simple-spinapp
+spec:
+  image: "ghcr.io/spinkube/containerd-shim-spin/examples/spin-rust-hello:v0.13.0"
+  replicas: 1
+  executor: spintainer
+```
+
+## How the spintainer executor works
+
+The spintainer executor executes your Spin application in a container created from the image specified by `.spec.deploymentConfig.spinImage`. The container image must have a Spin binary be the [entrypoint](https://docs.docker.com/reference/dockerfile/#entrypoint) of the container. It will be started with the following args.
+
+```
+up --listen {spin-operator-defined-port} -f {spin-operator-defined-image} --runtime-config-file {spin-operator-defined-config-file}
+```
+
+For ease of use you can use the images published by the Spin project [here](https://github.com/fermyon/spin/pkgs/container/spin). Alternatively you can craft images for your own unique need.