How to measure Docker build steps duration?

Question

Is it possible to configure Docker to output timing for the build of a Dockerfile?

We run a medium sized development team and would like to collect statistics on the

Answer 1

Time whole build

time docker build .

Time steps of build

docker build . | while read line ; do echo "$(date)| $line"; done;

Output

Wed  5 Sep 2018 19:12:22 BST| Sending build context to Docker daemon  27.65kB
Wed  5 Sep 2018 19:12:22 BST| Step 1/19 : FROM centos:centos7
Wed  5 Sep 2018 19:12:22 BST| ---> 49f7960eb7e4
...

You can improve the results by only outputting the "Step ?/? :" lines, like so:

docker build . | grep "^Step" | while read line ; do echo "$(date +%s)| $line"; done;

Output

1536171476| Step 1/19 : FROM centos:centos7
1536171476| Step 2/19 : ENV TERM xterm
1536171476| Step 3/19 : RUN *** omitted ***
1536171476| Step 4/19 : RUN *** omitted ***
1536171476| Step 5/19 : COPY *** omitted ***
1536171476| Step 6/19 : RUN *** omitted ***
1536171476| Step 7/19 : COPY *** omitted ***

JSON output

You can make this into a script if you wanted to run in a CI/CD pipeline, or add to your developer tools.

#!/bin/bash
#   script: time-docker-build.sh
#
#   All command line arguments are passed to docker build command.
#
#   usage: ./time-docker-build.sh
#

DATE_FORMAT="+%s"

(
    # Output START line
    echo "$(date $DATE_FORMAT) | - 0 - START"

    docker build $* . | \
        grep "^Step" | \
        while read line ;
        do
            # Output build output prefixed with date
            echo "$(date $DATE_FORMAT) | $line";
        done;

    # Output END line
    echo "$(date $DATE_FORMAT) | - -1 - END"
) | (
    # Generate JSON array output.
    #   - START is step: 0
    #   - END is step: -1

    echo "["
    FIRST_RUN=true
    while read line ;
    do
        [[ -z "$FIRST_RUN" ]] && echo ","   # if not first line, print ','

        lineArray=($line)
        time="${lineArray[0]}"          # step is 0th
        step="${lineArray[3]}"          # step is 2nd
        cmd="${lineArray[@]:5}"         # cmd is everything after 5th

        stepNum=${step/\/*/}
        escapedCmd="${cmd//\"/\\\"}"    # escape all double quotes '"'

        echo "  {"
        echo "    \"time\": $time,"
        echo "    \"step\": $stepNum,"
        echo "    \"cmd\": \"$escapedCmd\""
        echo -n "  }"

        unset FIRST_RUN
    done
    echo
    echo "]"
)

Output

bash-3.2$ ./time-docker-build.sh
[
  {
    "time": 1536174052,
    "step": 0,
    "cmd": "START"
  },
  {
    "time": 1536174052,
    "step": 1,
    "cmd": "FROM centos:centos7"
  },
  {
    "time": 1536174052,
    "step": 2,
    "cmd": "ENV TERM xterm"
  },

Script is available as a gist here:

https://gist.github.com/philpoore/05eca572f3aadf70f529c470ac679147