150Mb more memory used with node 8.10.0 than 10.13.0

[teeparham]

The memory usage for a single Hobby dyno rails web app was 150Mb higher without the heroku/nodejs buildpack.

A) with heroku/nodejs

Memory: 350Mb

Buildpacks:

1. https://github.com/gaffneyc/heroku-buildpack-jemalloc.git
2. https://github.com/cyberdelia/heroku-geo-buildpack.git
3. heroku/nodejs # <-----------------------------------------
4. heroku/ruby

Deploy log:

remote:        Downloading and installing node 10.13.0...

B) without heroku/nodejs

Memory: 500Mb

Buildpacks:

1. https://github.com/gaffneyc/heroku-buildpack-jemalloc.git
2. https://github.com/cyberdelia/heroku-geo-buildpack.git
3. heroku/ruby

Deploy log:

remote: -----> Installing node-v8.10.0-linux-x64

The rails app uses:

  * execjs (2.7.0)
  * sprockets (3.7.2)
  * sprockets-rails (3.2.1)

[elaine-jackson]

What optimizations / differences are in the nodejs build back that could be added to the Ruby build pack for it's Node.js support?

[schneems]

Can you please open a support ticket so we can look at your app? https://help.heroku.com search for "node higher memory use". Are you using node at runtime in your ruby app?

cc/ @jmorrell

[schneems]

This is relevant since we recently bumped the node version to 10.x on the Ruby buildpack on master, but it hasn't been deployed yet #831

[teeparham]

The ruby app is not using node at runtime. That's why I tried to remove the node buildpack. Yes, I'll open a ticket.

[schneems]

Wanted to mention the ultimate root cause if anyone stumbles upon this thread.

The heroku/nodejs buildpack will set a default value for WEB_CONCURRENCY however the Ruby buildpack will not. So if someone has an app with a line like this in their config:

workers Integer(ENV.fetch("WEB_CONCURRENCY") { 1 })

Then they would expect the default value to be 1 when in reality the value is set by the node buildpack.

This can be resolved by not using the node buildpack or by explicitly setting the WEB_CONCURRENCY value:

$ heroku config:set WEB_CONCURRENCY=1