a bit o' spruce, from http://play.spruce.cf

spruce.json

{"flavor":"1.13.0","prune":["meta"],"env":["HOME=/home/user"],"cherry_pick":[],"yaml":[{"filename":"mjolnir.yml","contents":"--- # mjolnir.yml\nmeta:\n  env: prod\n\nclusters:\n- name: mjolnir\n  servers:\n  - 10.0.1.1\n  - 10.0.1.2\n  env: (( grab meta.env ))\n  instances: 2\n\n"},{"filename":"file2.yml","contents":"--- # hammer\nclusters:\n- name: hammer\n  env: (( grab meta.env ))\n  \u003c\u003c: (( grab meta ))\n  servers:\n  - 10.1.1.1\n  - 10.1.1.2\n  - 10.1.1.3\n  instances: 3\n\n"},{"filename":"file3.yml","contents":"--- # final\nsite_list:\n- (( concat \"mjolnir-\" clusters.mjolnir.env ))\n- (( concat \"hammer-\" clusters.hammer.env ))\n\nsites: (( join \",\" site_list ))\n\nfootprint: (( calc \"(clusters.mjolnir.instances + clusters.hammer.instances) * 2048\" ))\n\n"}],"skip_eval":false,"fallback_append":false,"go_patch":false,"debug":false,"trace":false}