Automatic client updates

[yourheropaul]

Now that we have cross-compiled, versional releases of the client based on GitHub releases, it seems like we're pretty close to being able to automatically update the client when a new version becomes available.

There is a solid Go package for accomplishing the actual binary replacement based on GH releases, which is compatible with the pattern we're using. There's also https://github.com/jpillora/overseer.

Behaviour

Since there are (or will be) two recommended ways of running the client - as a native binary and via docker - there are to general flavours to auto-updating:

Native binary:

• When executed, checks for a new version. If a new version if available, downloads it and then prompts the user to restart.
• During execution, checks for newer versions and notifies the user (perhaps via the log) that a newer version is available.

Docker image:

• When started, checks for a new version and downloads it if available. The newest version is then executed.
• If a new version becomes available during execution, it's downloaded and the binary is restarted so that the new version is now running.
• This may mean that compiling the binary and shipping it inside the Docker image is unnecessary; it might be better to ship the image with no binary and have it download the newest version on execution.

Restrictions

Legal

For legal reasons, we cannot administer the network. That means:

• Auto updates must be optional
• It must be possible for other people to provide update sources. It's acceptable for us to provide an official source, but it has to be easy to create and use an unofficial one.

Network config

We will run multiple networks (live net, master testnet, internal testnet) which also need to automatically update. That means clients must be able to pick the appropriate binaries -- not just the latest ones.

Other possible implications

• If the updated works nicely, we could exclude from the validation pool valdiators running clients under some constantly-updated minimum version.
• It's conceivably possible to exclude nodes running some constantly-updated minimum version from even joining the network.

[jmatosp]

going to do some poc

[yourheropaul]

The first part of this (the binary updating itself) is working. I'm moving this to the next milestone for the other parts.

[jmatosp]

@yourheropaul

Can we just RUN an update on docker start?

[yourheropaul]

@jmatosp: That's a good first step, but it would be idea if the binary could (optionally) auto-update itself while running and then exit, and the docker image could restart it. Then we'd have truly automated live updates for those who want them.