Add support for arbitrary writable volume mounts during pack build

[jromero]

Summary

This PR adds support to volume mount at any location during pack build. It additionally adds support for writable mounts (rw).

Output

After

pack build --help

$ ./out/pack build --help
Generate app image from source code

Usage:
  pack build <image-name> [flags]

Flags:
  -B, --builder string              Builder image (default "gcr.io/paketo-buildpacks/builder:base")
  -b, --buildpack strings           Buildpack reference in the form of '<buildpack>@<version>',
                                      path to a buildpack directory (not supported on Windows),
                                      path/URL to a buildpack .tar or .tgz file, or
                                      the name of a packaged buildpack image
                                    Repeat for each buildpack in order,
                                      or supply once by comma-separated list
  -R, --buildpack-registry string   Buildpack Registry URL
      --clear-cache                 Clear image's associated cache before building
  -D, --default-process string      Set the default process type
  -d, --descriptor string           Path to the project descriptor file
  -e, --env stringArray             Build-time environment variable, in the form 'VAR=VALUE' or 'VAR'.
                                    When using latter value-less form, value will be taken from current
                                      environment at the time this command is executed.
                                    This flag may be specified multiple times and will override
                                      individual values defined by --env-file.
      --env-file stringArray        Build-time environment variables file
                                    One variable per line, of the form 'VAR=VALUE' or 'VAR'
                                    When using latter value-less form, value will be taken from current
                                      environment at the time this command is executed
  -h, --help                        Help for 'build'
      --network string              Connect detect and build containers to network
      --no-pull                     Skip pulling builder and run images before use
  -p, --path string                 Path to app dir or zip-formatted file (defaults to current working directory)
      --publish                     Publish to registry
      --run-image string            Run image (defaults to default stack's run image)
      --trust-builder               Trust the provided builder
                                    All lifecycle phases will be run in a single container (if supported by the lifecycle).
      --volume stringArray          Mount host volume into the build container, in the form '<host path>:<target path>[:<mode>]'.
                                    Repeat for each volume in order,
                                      or supply once by comma-separated list

Global Flags:
      --no-color     Disable color output
  -q, --quiet        Show less output
      --timestamps   Enable timestamps in output
  -v, --verbose      Show more output

mounting a custom lifecycle

$ pack build my-bash-app -B cnbs/sample-builder:bionic --volume=/Users/javier.romero/dev/buildpacks/lifecycle/out/linux/lifecycle/:/cnb/lifecycle/ -p ~/dev/buildpacks/samples/apps/bash-script/
Warning: Using untrusted builder with volume mounts. If there is sensitive data in the volumes, this may present a security vulnerability.
bionic: Pulling from cnbs/sample-builder
Digest: sha256:3665853288be6c7df936f53dd8fccea10d22785c3015aec4dd49ab44f9c3a7bb
Status: Image is up to date for cnbs/sample-builder:bionic
bionic: Pulling from cnbs/sample-stack-run
Digest: sha256:4c51a26b0546508ccd6f2d14753d041b595b3f9bceef77f4bb969e06c66474a4
Status: Image is up to date for cnbs/sample-stack-run:bionic
Warning: Mounting to a sensitive directory /cnb/lifecycle/
0.8.0: Pulling from buildpacksio/lifecycle
Digest: sha256:48dfb79e342fdeb68a1bf310b33b349269b2919cb5029e0b7184b84e82fc0bb3
Status: Image is up to date for buildpacksio/lifecycle:0.8.0
===> DETECTING
[detector] samples/bash-script 0.0.1
===> ANALYZING
[analyzer] Previous image with name "index.docker.io/library/my-bash-app:latest" not found
===> RESTORING
===> BUILDING
[builder] ---> Hello World buildpack
[builder] ---> Hello Bash Script buildpack
[builder] 
[builder] Here are the contents of the current working directory:
[builder] .:
[builder] total 16
[builder] drwxr-xr-x 2 cnb  cnb  4096 Aug  5 18:50 .
[builder] drwxr-xr-x 1 root root 4096 Aug  5 18:50 ..
[builder] -rwxr-xr-x 1 cnb  cnb   738 Apr  6 23:13 app.sh
[builder] -rw-r--r-- 1 cnb  cnb   202 Apr  6 23:13 project.toml
===> EXPORTING
[exporter] Adding layer 'launcher'
[exporter] Adding 1/1 app layer(s)
[exporter] Adding layer 'config'
[exporter] *** Images (d1b9f852dd37):
[exporter]       index.docker.io/library/my-bash-app:latest
Successfully built image my-bash-app

Documentation

• Should this change be documented?
  • Yes, see Document volume mounting for pack docs#181
  • No

Related

Resolves #764

[codecov]

Codecov Report

Merging #778 into main will decrease coverage by 0.01%.
The diff coverage is 85.72%.

@@            Coverage Diff             @@
##             main     #778      +/-   ##
==========================================
- Coverage   74.75%   74.74%   -0.00%     
==========================================
  Files          77       77              
  Lines        5164     5174      +10     
==========================================
+ Hits         3860     3867       +7     
- Misses        999     1002       +3     
  Partials      305      305              

Flag	Coverage Δ
#os_linux	77.25% <100.00%> (+0.04%)	⬆️
#os_macos	73.17% <100.00%> (+0.05%)	⬆️
#os_windows	72.99% <57.15%> (-0.14%)	⬇️
#unit	74.74% <85.72%> (-<0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[dfreilich]

Looks great. Should we have a warning that this may not work on other OSs?

[dfreilich]

👍

[jromero]

Looks great. Should we have a warning that this may not work on other OSs?

The only one I know of in which this may not work is Windows (WCOW) but honestly haven't thoroughly tested it in LCOW.

[ameyer-pivotal]

Looks great. Should we have a warning that this may not work on other OSs?

The only one I know of in which this may not work is Windows (WCOW) but honestly haven't thoroughly tested it in LCOW.

@jromero for WCOW, the solution would be fairly simple. Just use the mounts.NewParser(mounts.OSWindows) parser and users would just need to provide the target location as c:/path/in/container.

[jromero]

Looks great. Should we have a warning that this may not work on other OSs?

The only one I know of in which this may not work is Windows (WCOW) but honestly haven't thoroughly tested it in LCOW.

@jromero for WCOW, the solution would be fairly simple. Just use the mounts.NewParser(mounts.OSWindows) parser and users would just need to provide the target location as c:/path/in/container.

@ameyer-pivotal Thank you. If I'm not mistaken this will be taken care of as part of #739