incorrect detection of npm-start buildpacks leads to invalid entrypoint

[Baran Dalgic]

What happened?

I am trying to build a simple nodejs application using the paketo and noticed that the npm-start buildpack sets an invalid entrypoint.

• What were you attempting to do?

Build an image for https://github.com/shipwright-io/sample-nodejs/tree/main/source-build

• What did you expect to happen?

Since the source directory does contain an app.js, I expect it to be the entrypoint to the application as described in the paketo documentation.

• What was the actual behavior? Please provide log output, if possible.

The platform choses this buildpack which sets an invalid entrypoint to a non existing server.js.

===> ANALYZING
Previous image with name "node-bug-sample" not found
===> DETECTING
5 of 10 buildpacks participating
paketo-buildpacks/ca-certificates 3.0.1
paketo-buildpacks/node-engine     0.11.2
paketo-buildpacks/npm-install     0.6.2
paketo-buildpacks/node-module-bom 0.2.0
paketo-buildpacks/npm-start       0.6.1
===> RESTORING
===> BUILDING

Paketo CA Certificates Buildpack 3.0.1
  https://github.com/paketo-buildpacks/ca-certificates
  Launch Helper: Contributing to layer
    Creating /layers/paketo-buildpacks_ca-certificates/helper/exec.d/ca-certificates-helper
Paketo Node Engine Buildpack 0.11.2
  Resolving Node Engine version
    Candidate version sources (in priority order):
      package.json -> ">= 0.10.12"
      <unknown>    -> ""

    Selected Node Engine version (using package.json): 16.13.1

  Executing build process
    Installing Node Engine 16.13.1
      Completed in 6.701s

  Configuring build environment
    NODE_ENV     -> "production"
    NODE_HOME    -> "/layers/paketo-buildpacks_node-engine/node"
    NODE_VERBOSE -> "false"

  Configuring launch environment
    NODE_ENV     -> "production"
    NODE_HOME    -> "/layers/paketo-buildpacks_node-engine/node"
    NODE_VERBOSE -> "false"

    Writing profile.d/0_memory_available.sh
      Calculates available memory based on container limits at launch time.
      Made available in the MEMORY_AVAILABLE environment variable.

Paketo NPM Install Buildpack 0.6.2
  Resolving installation process
    Process inputs:
      node_modules      -> "Not found"
      npm-cache         -> "Not found"
      package-lock.json -> "Not found"

    Selected NPM build process: 'npm install'

  Executing build process
    Running 'npm install --unsafe-perm --cache /layers/paketo-buildpacks_npm-install/npm-cache'
      Completed in 845ms

  Configuring launch environment
    NPM_CONFIG_LOGLEVEL -> "error"

  Configuring environment shared by build and launch
    PATH -> "$PATH:/layers/paketo-buildpacks_npm-install/modules/node_modules/.bin"


Paketo Node Module Bill of Materials Generator Buildpack 0.2.0
  Resolving CycloneDX Node.js Module version
    Selected CycloneDX Node.js Module version: 3.0.7

  Executing build process
    Installing CycloneDX Node.js Module 3.0.7
      Completed in 254ms

  Configuring environment
    Appending CycloneDX Node.js Module onto PATH

  Running CycloneDX Node.js Module
    Running 'cyclonedx-bom -o bom.json'
      Completed in 316ms

Paketo NPM Start Buildpack 0.6.1
  Assigning launch processes
    web: node server.js

The error output when running the image:

node:internal/modules/cjs/loader:936
  throw err;
  ^

Error: Cannot find module '/workspace/server.js'
    at Function.Module._resolveFilename (node:internal/modules/cjs/loader:933:15)
    at Function.Module._load (node:internal/modules/cjs/loader:778:27)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:17:47 {
  code: 'MODULE_NOT_FOUND',
  requireStack: []
}

Build Configuration

• What platform (pack, kpack, tekton buildpacks plugin, etc.) are you
  using? Please include a version.

pack - 0.23.0

• What buildpacks are you using? Please include versions.

paketo-buildpacks/ca-certificates 3.0.1
paketo-buildpacks/node-engine 0.11.2
paketo-buildpacks/npm-install 0.6.2
paketo-buildpacks/node-module-bom 0.2.0
paketo-buildpacks/npm-start 0.6.1

• What builder are you using? If custom, can you provide the output from pack inspect-builder <builder>?

paketobuildpacks/builder:full

• Can you provide a sample app or relevant configuration (buildpack.yml,
  nginx.conf, etc.)?

https://github.com/shipwright-io/sample-nodejs/tree/main/source-build and run $DIR/source-build$ pack build node-bug-sample --builder paketobuildpacks/builder:full

Checklist

• I have included log output.
• The log output includes an error message.
• I have included steps for reproduction.

Further observations

The behaviour described in the paketo documentation is contributed by the node-start buildpack. The npm-start buildpack is falsely applied in this instance, because its detection criteria is the existence of a package.json file. However, that package.json file does not contain any start commands (pre-start, start...). Thus, it seems like the detection phase of this buildpack has to be extended to also check for a suitable start command. If not, then node-start should be preferred.