mini_sendmail is a tiny implementation of sendmail that can be copied in the Flywheel chroot on our customers’ instances. It is the interface that PHP talks to in order to send email. Our architecture looks like this:

|-----|        |---------------|        |---------|        |----------|
| PHP |  --->  | mini_sendmail |  --->  | postfix |  --->  | SendGrid |
|-----|        |---------------|        |---------|        |----------|

Below, you will find documentation on how to build our mini_sendmail package and update our Chef release with it.

To build this package, you need the GCC toolchain. Without doing a bunch of jumping through hoops, macOS only has access to the Clang toolchain, which has a different grammar for linking than GCC does. Since we host on Ubuntu, we have to build with GCC instead of Clang.

The easiest way to get going is to start with a new DigitalOcean droplet on our current version of Ubuntu. Once it’s provisioning, SSH into the box with whatever key you added to the box. Then, install Git with the following:

$ sudo apt-get update -q && sudo apt-get install -q -y git

After Git is installed, you should configure SSH so that you will be able to pull from this private repository. The easiest way to do this is to copy your SSH key from your laptop to the server.

Start a new terminal session on your computer and run this command, making sure to replace the template values (denoted like <VARIABLE>) with ones that match your configuration:

$ scp -i <KEY_TO_CONNECT_WITH> <KEY_TO_SEND> root@<DROPLET_IP>:~/.ssh

Alternatively, if you are security conscious, you can generate a new SSH key with the following:

$ ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -q -N “”
$ cat ~/.ssh/id_ed25519.pub

Then, add this SSH key to your GitHub account by copying the output of that last command into a new key on GitHub at:

https://github.com/settings/keys

After getting a key set up to pull from GitHub, you will want to start an SSH agent to hold that key for connecting. Run this command and enter the passphrase for your SSH key, if any:

$ eval $(ssh-agent)

One you have SSH and GitHub configured, you can clone this repository and run the setup script:

$ git clone [email protected]:getflywheel/mini_sendmail.git

The repository has a script that will install everything that you need to install and package

$ cd mini_sendmail && bin/setup

To build the executable, execute the following from within the Git repository:

$ make

This outputs the executable (mini_sendmail) in the root directory of the Git repository.

To run the tests we have written, run the following from within the Git repository root:

$ make test

To build the Debian package, run the following from within the Git repository root:

$ make package

This will build the package and place it in the parent directory above the Git repository root.

The VERSION file holds the version that will be embedded in the program. Increment it appropriately, then rebuild and make the package. The value that you put in VERSION should be greater than the last version, but otherwise we do not have a versioning schema.

We are currently distributing the package with Chef in the flywheel-apt cookbook. You will want to download the .deb package file to your local machine in order to update the Chef cookbook with the new version.

You will also need to update the version of the package in the mini_sendmail::default Chef cookbook.