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Sample supply buildpack for Cloud Foundry sidecars
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Part 3 - Supply buildpack for Cloud Foundry sidecars

Cloud Foundry sidecars are an additional process running inside your application container (see blog post). Cloud Foundry buildpacks allow the installation of additional software within your application container.

In this sample project, we use a buildpack to install a pre-compiled executable config-server, which is run within the application container as a sidecar.

Run through the demonstration below, and then see the highlights of parts of this repo/buildpack.


This demonstration of sidecars requires a Cloud Foundry running capi-release 1.79.0 or greater (for example cf-deployment v7.11.0 or higher).

CFDev deploys a version of Cloud Foundry that supports Sidecars.


cf v3-create-app app-using-config-server
cf v3-apply-manifest -f fixtures/rubyapp/manifest.yml
cf v3-push app-using-config-server -p fixtures/rubyapp
   -----> Installing config-server v0.0.1

If you view the logs you'll see the sidecar's output and the ruby app's output:

$ cf logs app-using-config-server --recent
[APP/PROC/WEB/0] ERR [2019-05-18 02:53:35] INFO  WEBrick 1.3.1
[APP/PROC/WEB/0] ERR [2019-05-18 02:53:35] INFO  ruby 2.4.6 (2019-04-01) [x86_64-linux]
[APP/PROC/WEB/0] ERR [2019-05-18 02:53:35] INFO  WEBrick::HTTPServer#start: pid=16 port=8080

But does it blend?

If we interact with our main app we see that it can now communicate with its sidecar to get some internally secret configuration.

$ curl -k
Hi, I'm an app with a sidecar!
$ curl -k

Obviously this is a silly example. No one put hyphens in their passwords.


Like part2-sidecar-buildpack, this project is first-and-foremostly a supply buildpack, which also includes an application for dev/testing/demonstration.

Unlike sample1, this project also includes the source code for config-server, as well as a script for compilation and storing to an AWS S3 bucket (scripts/

A supply buildpack can be used in addition to a normal buildpack to inject additional software/libraries/executables/files into the application droplet and runtime containers. This buildpack injects a pre-compiled executable config-server into the application droplet, which can then be run as a sidecar by the application.

A supply buildpack needs:

  • a bin/supply file
  • to be included in an application's manifest.yml list of buildpacks, but cannot be the last in that list.

Our sample application's manifest.yml specifies this buildpack as the first in the list. It references the buildpack by its HTTPS URI to the git repository. It could have also referenced an HTTPS URI to a .zip file, or the name of a pre-uploaded buildpack (as found in cf buildpacks list).

  - ruby_buildpack

The bin/supply can create/install files into a specific folder. This folder is provided as the first argument when bin/supply is executed during staging.

In sample1 we created a silly executable, but in sample2 we are downloading a pre-compiled executable from the Internet. We've stored the URL in .downloadurl file.

curl -sSf $(cat .downloadurl) -o $BUILD_DIR/config-server
chmod +x $BUILD_DIR/config-server

In order for this file to exist on the Internet, we added scripts/ It builds the Golang project for a 64-bit Linux architecture (to match the Linux containers used by Cloud Foundry).

cd src/config-server-sidecar
GOOS=linux GOARCH=amd64 go build -o "config-server-v${VERSION}" .

It uploads the artifact to an S3 bucket:

aws s3 cp \
  "src/config-server-sidecar/config-server-v${VERSION}" \

Finally, it updates the .downloadurl file in the buildpack repo so that the bin/supply staging command knowns how to fetch the pre-compiled binary.

The S3 bucket has been made read-only for all files, so that anyone can use this buildpack.


    "Version": "2008-10-17",
    "Statement": [
            "Sid": "AllowPublicRead",
            "Effect": "Allow",
            "Principal": {
                "AWS": "*"
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::sample1-sidecar-buildpack/*"


The sample app in fixtures/rubyapp and its example of running a fictional config-server sidecar originate from

The config-server executable also comes from the same repo at

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