When your building your images at the first time probably you have encounter the issue that relates the uid and gid that ends it up in conflics with your host machine permissions, this is true when you are planning to mount a volumen to your container. This section [0] provides you an idea of how to deal with this.

[0] https://github.com/nodejs/docker-node/blob/master/docs/BestPractices.md#non-root-user