Goal

We want the ecs-cli-v2 to be able to parse healthcheck options from the user’s Dockerfile. There are total of four options you can specify (otherwise will result into default values) and an optional command.

Overview

Options

• interval
• timeout
• start-period
• retries

Types of Healthcheck formats

1. No command

HEALTHCHECK --interval=5m --timeout=3s

2. No options

HEALTHCHECK CMD curl -f http://localhost/ || exit 1

3. Options and command in the same line

HEALTHCHECK --interval=5m --timeout=3s CMD curl -f http://localhost/ || exit 1

4. Options and command in different lines

HEALTHCHECK --interval=5m --timeout=3s \
  CMD curl -f http://localhost/ || exit 1

5. No healthcheck

HEALTHCHECK NONE

Design Proposal

Building on top of the parsing ports on a Dockerfile #747, we can create a Healthcheck struct to group all of the options and command. In addition, a separate method for parsing Healthcheck.

Programming Model

type HealthCheck struct {
  interval uint16
  timeout uint16
  startPeriod uint16
  retries uint16
  command string
}

func parseHealthcheck(line string) []healthcheck {

}

Parsing Method

Currently, the way ecs-cli-v2 reads the user's Dockerfile by scanning line by line. We can use regex to parse the health check options as they will always follow the same format.

Example

healthcheckRegexPattern := "--([^\\s]+)" // this will grab all strings that start with --

We can also use regex to parse out the command

healtchcheckCMDRegexPattern := "CMD.*" //this will grab CMD until the end of the line

Issue

An issue arises when CMD is put on a different line (No. 4 on Types of Healtcheck formats). Because the scanner reads one line at a time, it will not be able to pick up CMD on the second line. I propose a healthcheckCMD flag where it will insert the following CMD line into the healthcheck struct if command in the healthcheck struct is empty and if the CMD line is right after HEALTHCHECK.