Created
December 23, 2016 16:34
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amazon emr detect master node and run an s3 script
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| #!/usr/bin/python | |
| # via https://forums.aws.amazon.com/thread.jspa?messageID=737877 | |
| # see also | |
| # https://forums.aws.amazon.com/thread.jspa?messageID=758242 | |
| #''' | |
| #Evaluate logical tests against the instances.json file | |
| #''' | |
| # understand isMaster=true and isMaster!=true | |
| # does NOT understand isMaster=false and isMaster!=false | |
| import sys | |
| import os | |
| import subprocess | |
| import re | |
| import json | |
| INSTANCE_FILE = "/mnt/var/lib/info/instance.json" | |
| PROP_RE = re.compile(r'(?P<prop>[A-Za-z_]+)(?P<op>(!=)|(={1,2}))(?P<val>\w+)') | |
| def is_boolean(val): | |
| return re.match('(true)|(false)', val, re.I) is not None | |
| def check_truthiness(val): | |
| if val is None: | |
| return False | |
| elif type(val) == bool: | |
| return val | |
| elif type(val) == str: | |
| return re.match('true', val, re.I) is not None | |
| else: | |
| return False | |
| def match_expr(expr): | |
| try: | |
| with open(INSTANCE_FILE) as f: | |
| props = json.load(f) | |
| except IOError as e: | |
| # file will not exist when testing on a non-emr machine | |
| print("This script can only be run on an emr machine: " + str(e)) | |
| return False | |
| parsed = PROP_RE.match(expr) | |
| if not parsed: | |
| print("Please pass a logical expression of form 'Property=true' or 'Property!=val'") | |
| return False | |
| prop = props.get(parsed.group('prop')) | |
| if is_boolean(parsed.group('val')): | |
| if parsed.group('op')[0] == '!': | |
| return not check_truthiness(prop) | |
| else: | |
| return check_truthiness(prop) | |
| else: | |
| if parsed.group('op')[0] == '!': | |
| return prop != parsed.group('val') | |
| else: | |
| return prop == parsed.group('val') | |
| if len(sys.argv) < 3: | |
| print("You must pass in at least 2 args: a condition, and an s3 url of a script to run.") | |
| print("Usage: run-if isMaster=true s3://<MY-BUCKET>/my-script.sh arg1 arg2") | |
| sys.exit(1) | |
| elif sys.argv[2][:5] != 's3://': | |
| print("The script passed in must be expressed as a valid s3 url!") | |
| print("Usage: run-if isMaster=true s3://<MY-BUCKET>/my-script.sh arg1 arg2") | |
| sys.exit(1) | |
| if match_expr(sys.argv[1]): | |
| local_name = os.tempnam('./') | |
| subprocess.call(['aws', 's3', 'cp', sys.argv[2], local_name]) | |
| os.chmod(local_name, 0500) | |
| result = subprocess.call([local_name] + sys.argv[3:]) | |
| sys.exit(result) | |
| else: | |
| print("Condition " + sys.argv[1] + " is false, so not running command.") | |
| sys.exit(0) |
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