Docker and Heroku use the exact same sandboxing technology under the hood (Linux namespaces and cgroups). This is not surprising since Docker came out of Dotclo

Docker and Heroku use the exact same sandboxing technology under the hood (Linux namespaces and cgroups). This is not surprising since Docker came out of Dotcloud, a direct Heroku competitor. The pros and cons of linux namespaces have been extensively discussed, it's no silver bullet but when used properly is quite robust and is rapidly gaining industry recognition.