Is there any service like Travis CI or CircleDI that lets you add your own slaves? Jenkins let's you turn a box into a slave by running a simple jar file.
It would be nice if CircleCI or Travis CI offered as that would mean not having to pay them for instances and instead turning AWS instances into CircleCI/Travis slaves at a lower per-instance cost. I'd still be happy to pay for their website and for their system managing the slaves.
It has always been avoided in Jenkins-based systems for security purposes. Traditionally, slaves could request that masters do pretty much anything, as Jenkins treated the master/slave relationship as one large system rather than isolated and restricted nodes.
This has gotten slightly better over time, but the default is still "slave is just another process alongside the master" – you need to setup any whitelisting of slave filesystem or execution permissions yourself.
It would be nice if CircleCI or Travis CI offered as that would mean not having to pay them for instances and instead turning AWS instances into CircleCI/Travis slaves at a lower per-instance cost. I'd still be happy to pay for their website and for their system managing the slaves.