We sped up your bluegreen deployments by adding more concurrency in flyctl v0.2.31! Bluegreen deploys previously did a lot of things sequentially and now they operate on up to 16 machines concurrently. That makes each step faster in your deployments: faster creation of the new green machines, faster cordon/uncordon, faster stopping and destroying old blue machines.
We saw a 3 minute improvement in bluegreen deploy times with this change for a 100 machine app we have internally. It went from 4 minutes down to 1 minute. We saw a 2 minute improvement for a 70 machine app going from 3 minutes down to 1 minute.
You can tune the amount of concurrency used with the new --max-concurrent flag. It uses 16 by default.
We hid the --immediate-max-concurrent flag documentation, as it is replaced by --max-concurrent. --immediate-max-concurrent will continue to work and is an alternate way to set --max-concurrent.
Let us know if you have any issues in the replies below.