Automated node join script for Teleport

This is an automated node join script for Teleport, which does the following:

checks for an existing Teleport process, data directory, config file or Teleport binaries (and provides details how to clean up if any of these are present)
tests connectivity to the given Teleport server host and port
- using either nc, telnet or /dev/tcp if available - if none of these are available this step is skipped
detects OS, distribution, architecture and appropriate Teleport package format, then downloads this package to a temporary directory and installs it
- tar for tarball extraction if needed
- dpkg for .deb installs
- dnf, yum or rpm for .rpm installs
generates a Teleport config to set up a node and writes it to disk
installs and starts Teleport
- via systemd on Linux
- via launchctl on MacOS
cleans up downloaded archives afterwards

Things it doesn't do (yet):

validate the checksum of the downloaded Teleport artifact against the published checksum

Supported operating systems, architectures and distributions

Linux
- Architectures
  - i386
  - x86_64
  - armv7l
  - aarch64 (no Teleport binaries available yet)
- Any Debian-based distribution
  - Debian 8+
  - Ubuntu 18.04+
    - uses .deb package
- Any CentOS-based distribution
  - CentOS 6+*
  - RHEL 6+*
    - CentOS 6 and RHEL 6 will use the special centos6 tarball package to handle the lower glibc version.
  - Fedora 27+
  - Amazon Linux 2+
    - uses .rpm package
- Any other distribution
  - uses .tar.gz tarball package
macOS
- Architectures
  - x86_64
  - aarch64
- macOS 12.0+
  - uses .tar.gz tarball package

Arguments

Required arguments:

Flag	Description	Example value	Required
`-v`	Teleport version	`4.3.5`	yes
`-h`	Hostname for the Teleport Proxy Service	`teleport.example.com`	yes
`-j`	A valid node join token	`ool7ahpo4thohmeuS1gieY7laiwae7oo`	yes
`-c`	The CA pin hash of the cluster being joined	`sha256:6abdd3a143a230fd31c9706d668bba3ee25a6e0eec54fcd69680c1ec0530fe9c`	yes
`-p`	Port connect to on the Teleport Proxy Service	`3080`	no

If any of these arguments is not provided via CLI flags, they will be requested interactively at runtime.

Optional extra flags:

Flag	Description	Example value	Required
`-q`	Enable quiet mode	n/a	no
`-l`	Write logs to file	`/var/log/teleport-node-installer.log`	no

Example usage

$ bash ./install.sh \
    -j ool7ahpo4thohmeuS1gieY7laiwae7oo \
    -c sha256:6abdd3a143a230fd31c9706d668bba3ee25a6e0eec54fcd69680c1ec0530fe9c \
    -h teleport.example.com \
    -p 3080 \
    -v 4.3.5