Add Redis set-up to Ruby script

[lcreid]

• Get a stock 18.04 box
• Run rails-5-jade set-up script with the right arguments
• See where all the Redis files are at
• See if Redis config is set up for systemd -- no, it's not. Well, actually it is set up to start running automatically and all.
• Configure Redis to run for a different database for each user
• Try it out until it's right
• Write test cases for scripted version
• Refactor a bit if necessary
• Write the code to build Redis support

[lcreid]

File locations:

/etc/redis/redis.conf
/lib/systemd/system/redis-server.service
/var/run/redis.pid
logfile /var/log/redis/redis-server.log
dbfilename dump.rdb
dir /var/lib/redis

You can include config files in other config files, so for example, we could create a custom config file, include the default config file, then change the parameters we want to change in the custom config file.

[lcreid]

The Redis folks make a lot of arguments against using multiple databases as a way to share Redis, e.g. https://redis.io/commands/select. The fact that the databases are numbered, not named, makes it a bit inconvenient to automate the set-up as well. You would have to figure out which number database had been assigned to which application.

[lcreid]

If we were to run an instance of Redis for each application, the question is how? If each instance is run as redis:

• The systemd configuration doesn't have to set user and group
• we may get away with changing fewer defaults
• It may be easier to re-use the default config file. It's 640
• The ownership of the pipe has to be configured and/or the application user has to be added to theredis group. Probably both, as we would need to write the pipe

If we run as separate users:

• The systemd configuration has to set user and group
• We have better security (the pipe is only accessible to the application that uses it). We could even make the pipe 600
• Shared locations have to be set up for everything, under the right user and group
• The application user doesn't need another group (although we need it if we want to read the default config file)

the configuration would be easier if we didn't have to change the user (I think).