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Best practices

Naming conventions​

Prefer single word over plural.

It is better to leverage semantics of lets as an intention to do something. For example it is natural saying lets test or lets build something.

bad

lets runs

good

lets run

bad

lets tests

good

lets test

Default commands​

If you have many projects (lets say - microservices) - it would be great to have one way to run and operate them when developing

  • run command - the main purpouse of this command is to run all in once. If all projects has this command its easier to remember.
  • test command - each projects should have a tests and a way to run them, either one file or all tests at once
  • init command - some kind of project initialization - creates missing files, dirs for developer, checks permissions, login to docker registry, checks inotify limits for tools such as webpack and other file watchers.

Split lets.yaml when it becomes big.​

If lets.yaml became big, it may be great to split it in a smaller, more specific files using mixins directive. For example:

  • lets.yaml
  • lets.test.yaml
  • lets.build.yaml
  • lets.frontend.yaml
  • lets.i18n.yaml

In each of these files we then hold all specific tasks.

Use checskums​

Checksums can help you decrease amount of task executions. How ? Lets see.

Suppose we have js project and we obviously holding all dependencies in package.json. Also we are using Docker for reproducible development environment.

Dockerfile

FROM alpine:3.8

WORKDIR /work

COPY package.json .

RUN npm install

CMD ["npm start"]

What if we want to rebuild docker image every time we changed dependency ?

lets.yaml

shell: bash

commands:
  run:
    depends: 
      - build
    cmd: docker-compose up application

  build:
    checksum:
      - package.json
    persist_checksum: true  
    cmd: |
      if [[ ${LETS_CHECKSUM_CHANGED} == true ]]; then 
        docker-compose build application
      else
        Image is up to date
      fi

As you can see, we execute build command each time we execute run command (depends).

persist_checksum will save calculated checksum to .lets directory and all subsequent calls of build command will read checksum from disk, calculate new checksum, and compare them. If package.json will change - we will rebuild the image.

Initialize project using init​

You can use init keyword to write a script that will do some initialization on lets startup, like creating some dirs, configs or installing project dependencies.

By default, init runs each time the lets program is executed.

You can make init conditional, by simply creating a file and checking if it exists at the start of init script.

Example:

shell: bash

init: |
  if [[ ! -f .lets/init_done ]]; then
    echo "calling init script"
    touch .lets/init_done
  fi

In this example we are checking for .lets/init_done file existence. If it does not exist, we will call init script and create init_done file as a marker of successfull init script invocation.

We are using .lets dir here because this dir will be created by lets itself and is generally a good place to create such files, but you are free to create files with any name and in any directory you want.