mlaunch: check on launch if dbpath exists about mtools

[gianpaj]

What do you mean by compare startup options?

I think the main use case (internally) is to launch a set of nodes (repl or cluster) for a specific customer or bug/feature.

That usually means cd into a new directory and running mlaunch, which by default, means using the current path as dbpath.

I agree we need to show a warning if there is already a dbpath with databases in it, but not sure about exiting since it's not going to be overwritten unless an client is connecting to the db.

What about also using colors, something like this:

see also http://docs.fabfile.org/en/1.6/api/core/colors.html

[rueckstiess]

yes, but I just happened to start mlaunch in the same directory where I started it previously but with a different configuration (sharded vs. replica set) and that doesn't go so well. In the data/ folder there is actually a hidden file called .mlaunch_startup which contains all the startup options. We can compare that to the current startup options and see if they are compatible or not.

mlaunch --restore by the way reads these startup options and runs them again, so you always get the same configuration.

Color would be good but I don't know how to do that. Does it require a different shell? I'd like it to work on all kinds of shells, including bash.

PS: Should open a different feature request for the color output for all command line tools.

[gianpaj]

Oh I didn't know we had those start options.
And yeah now I get your point. Erroring out makes sense if it was a replica node first and now you are starting a config server with the same dbpath.

But not sure how did you managed that, since the dbpaths are different:
mlaunch --single uses:

• ./data/db

mlaunch --replicaset uses:

• ./data/replset/rs1/db
• ./data/replset/rs2/db
• ./data/replset/rs3/db

mlaunch --sharded 2 --config 1 --single uses these:

• ./data/shard01/db
• ./data/shard02/db
• ./data/config/db

Same for using custom path:
mlaunch --single ./crapdata

• ./crapdata/data/db

mlaunch --replicaset ./crapdata

• ./crapdata/data/replset/rs1/db
• ./crapdata/data/replset/rs2/db
• ./crapdata/data/replset/rs3/db

[gianpaj]

What could happen is in the case you have a replicaset with 3 nodes first and then you want 4. The fourth is not going to be added to the set and we should exit with an error message

[stennie]

This issue describes behaviour of mlaunch pre-#148. mlaunch --restore no longer exists and mlaunch start will report "A different environment already exists" if you try to init into an existing environment.