Skip to main content
The watch command (truss chains watch) combines the best of local development and full deployment. watch lets you run on an exact copy of the production hardware and interface but gives you live code patching that lets you test changes in seconds without creating a new deployment. To use truss chains watch:
  1. Push a chain in development mode with truss chains push --watch SOURCE. This creates a development deployment and starts watching in one step. You can also create the deployment separately and then run truss chains watch SOURCE to attach the watcher.
  2. Each time you edit a file and save the changes, the watcher patches the remote deployments. Updating the deployments might take a moment, but is generally much faster than creating a new deployment.
  3. You can call the chain with test data using cURL or the playground dialogue in the UI and observe the result and logs.
  4. Iterate steps 2. and 3. until your chain behaves in the desired way.
By default, watch keeps your development Chainlets warm so they don’t scale to zero while you iterate. On startup, the watcher wakes any scaled-to-zero Chainlets, waits for them to be ready before applying the first patch, then keeps them warm for the rest of the session. This avoids the readiness wait and the occasional patch failures that happen when a Chainlet falls asleep between edits. The --no-sleep flag controls this keepalive and is on by default. To let idle Chainlets scale to zero during a long watch session, opt out with truss chains watch my_chain.py --no-sleep=false. When you watch through push, pass --watch-no-sleep=false instead: truss chains push my_chain.py --watch --watch-no-sleep=false.

​
Selective watch

Some large ML models might have a slow cycle time to reload (for example, if the weights are huge). For this case, we provide a “selective” watch option. For example, if your chain has such a heavy model Chainlet and other Chainlets that contain only business logic, you can iterate on those, while not patching and reloading the heavy model Chainlet.
This feature is useful for advanced use cases, but must be used with caution. If you change the code of a Chainlet not watched, in particular I/O types, you get an inconsistent deployment.
Add the Chainlet names you want to watch as a comma-separated list:
Terminal
truss chains watch ... --experimental-chainlet-names=ChainletA,ChainletB