Docker Pull under the hood

Familiar with Docker, and looking for more specific information about when images get pulled or updated in Tugboat? Here’s what you need to know about docker pull under the hood:

When does Tugboat pull a Docker image?

Tugboat doesn’t pull the images in your config file every time you open a pull request, or refresh a Preview; it only does a docker pull (under the hood) when:

  • You build a Preview from scratch (without using a Base Preview)
  • You Rebuild a Preview that was not built from a Base Preview

Otherwise, Tugboat relies on the images you pulled when the Preview was first created; Preview Actions like Refreshing a Preview, Cloning a Preview, or automatically generating a Preview from a pull request when you’re using a Base Preview - those things all keep the Docker images you referenced when you first built the Preview.

When does Tugboat update a Docker image?

Because Tugboat pulls your Docker images at the beginning of the Preview build process, it won’t docker pull an updated image unless you kick off the Preview build process from scratch again.

For more info, see: Why Build phases matter.

If your Tugboat Preview isn’t pulling your latest Docker image tag, it might be because you’re building from a Base Preview. If that’s the case, you’ll need to Rebuild your Base Preview, which executes an API call to docker pull under the hood to grab the image tag referenced in your config file. If that still doesn’t get you the image you expect, check your config file to see which image tag you’re pulling; you may need to change the reference to latest, or a specific image tag, to get the result you want.