> For the complete documentation index, see [llms.txt](https://docs.terrakube.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.terrakube.io/2.34.0/run-terraform/workspaces/run-triggers.md).
# Run Triggers
A run trigger links two workspaces in the same organization: when the **source** workspace finishes a run that changed infrastructure, Terrakube queues a run in the **destination** workspace. Use it when one workspace consumes the outputs of another, for example a VPN workspace that reads a VPC workspace's outputs, so the dependent workspace does not silently drift.
{% hint style="info" %}
Available from Terrakube 2.34.0.
{% endhint %}
```mermaid
flowchart LR
vpc[vpc] -->|apply changed state| vpn[vpn]
vpc --> dns[dns]
vpn --> app[app]
dns --> app
```
Applying `vpc` queues runs in `vpn` and `dns`. When both of those apply, `app` runs after each.
### Configure a trigger
Open the destination workspace and select **Run Triggers** in the workspace menu.
* **Runs after** lists the workspaces whose applies start a run here. Add a source workspace, optionally choose a template (otherwise the destination's default template is used), and toggle a trigger on or off.
* **Triggers** lists the workspaces that run after this one. It is read-only here; change those from the other workspace.
Runs started this way say so in the run header and link to the upstream run.
The Run Triggers page of a workspace
### What fires a trigger
* Only a run that **applies, destroys or runs custom scripts** fires a trigger. A plan-only run fires nothing.
* If the destination is locked or busy, its run is queued rather than skipped.
* Triggers cascade: a destination can itself be the source of other triggers.
### Rules
* You need manage rights on the destination workspace, and must be able to see the source.
* Terrakube rejects a trigger that would create a loop, and names the path in the error.
* The two workspaces of a trigger cannot be changed once created. Delete it and create another.
### Limits
Two safety bounds, set on the API:
| Property | Default | Meaning |
| --------------------------------------------------- | ------- | ---------------------------------------------- |
| `io.terrakube.run-trigger.max-cascade-depth` | `10` | Longest chain of runs started by one apply. |
| `io.terrakube.run-trigger.max-dependents-per-apply` | `20` | Most workspaces one apply can trigger. |
| `io.terrakube.run-trigger.enabled` | `true` | Turns run triggers off for the whole instance. |
Triggers are also available over the API as the `runTrigger` resource (`sourceWorkspace`, `destinationWorkspace`, `template`, `enabled`).
---
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