There are several caching mechanism. They are essential to achieve faster build and execution times.
Docker caching is achieved by careful orderding and grouping of statements in container definitions (Dockerfile).
Docker caching works by caching each step in the Dockerfile; if the step does not change, the cached version is used.
We try here to design the Dockerfiles in order to minimize cache invalidations: for example, we add the code at the very end of the build process (since the code changes frequently).
When you first run docker/run, the build can take some time (2-10 minutes depending on your computer and your Internet connection). Starting from second run, the build is going to take a lot less, as Docker caching starts to be effective. You're going to see a lot of lines like:
Step 2 : ENV TZ America/New_York
---> Using cache
---> 8f46e6131fa8
(notice the Using cache).
The most demanding build step of a node.js container is running yarn. Depending on your package.json, this step can take a lot of time (up to 5 minutes in some cases). We save the yarn cache over successive builds (we store it in a file called .yarn-cache.tgz). In order to get consistent installs across machines, Yarn needs more information than the dependencies you configure in your package.json. Yarn needs to store exactly which versions of each dependency were installed. This information is stored in the yarn.lock file. It is important to check this into source-control. Documentation