While we say "Docker is just one possible container runtime", are there other implementations used in production environments as of late 2019, and do they have different approaches? (while Docker being a console wrapper for LXC more or less, right).
Are there other implementations
Yes. The Container Runtime group of the Cloud-Native Computing Foundation has a list of runtimes:
- Kata Containers
- Nabla Containers
Do they have different approaches
While they cannot all be compared with each other directly, they all offer a way to provide a container runtime. In some cases, this runtime leverages the kernel, in others, they are in userspace. While some are explicitly proprietary, others are explicitly Open. Some are supported by large corporations (Google, IBM, Amazon, Alibaba), others by foundations or open source communities.
All of these are used in production, but perhaps vary in their popularity.