composer: Unknown SSL protocol error in connection to getcomposer.org:443

Previously working Docker build script that relies on composer failing randomly. This is happening right now, while posting this ticket, and has happened periodically over the past week with no relevant changes on our side.

My composer.json:

{
  "require": {
     "ext-mbstring": "*",
     "ext-gd": "*",
     "ext-mcrypt": "*"
  }
}

Output of composer diagnose:

Not possible to run.

When I run this command:

curl -sS https://getcomposer.org/installer | php && mv composer.phar /usr/local/bin/composer && cd /var/www/ && composer install --no-plugins --no-scripts

I get the following output:

curl: (35) Unknown SSL protocol error in connection to getcomposer.org:443

And I expected this to happen:

Installer script should download composer.phar to the current directly.

This usually works, but we periodically run into a problem where this build step fails. This happens both locally and on AWS via Dockerfile running under Convox.

We have attempted to use composer.phar download directly from the site locally, but in this case the SSL errors prevent packages from being loaded by composer.

It looks like a server configuration error in getcomposer.org, possibly related to the server’s system time since the error seems to resolve itself after an indeterminate period of time. Just a guess though.