I got this error trying to bootstrap a local environment:
versions:
ii juju 1.19.1-0ubuntu1~12.04.1~juju1 next generation service orchestration system
ii juju-core 1.19.1-0ubuntu1~12.04.1~juju1 Juju is devops distilled - client
ii juju-deployer 0.3.4-0ubuntu1~precise1~ppa1 Deploy complex stacks of services using Juju
ii juju-local 1.19.1-0ubuntu1~12.04.1~juju1 dependency package for the Juju local provider
uploading tools for series [precise trusty]
Logging to /home/juju/local/cloud-init-output.log on remote host
Bootstrapping Juju machine agent
8b5954bd7ef8fe11b2f5330a517c7263382ada1ad92bcfbbdec449b402563719 /home/juju/local/tools/1.19.1.1-precise-amd64/tools.tar.gz
2014-05-05 14:45:34 INFO juju.cmd supercommand.go:301 running juju-1.19.1.1-precise-amd64 [gc]
2014-05-05 14:45:34 DEBUG juju.agent agent.go:375 read agent config, format "1.18"
2014-05-05 14:45:34 INFO juju.provider.local environprovider.go:40 opening environment "local"
2014-05-05 14:45:34 DEBUG juju.cmd.jujud bootstrap.go:161 starting mongo
2014-05-05 14:45:34 DEBUG juju.cmd.jujud bootstrap.go:182 calling ensureMongoServer
2014-05-05 14:45:34 INFO juju.agent.mongo mongo.go:153 Ensuring mongo server is running; data directory /home/juju/local; port 37017
2014-05-05 14:45:34 INFO juju.agent.mongo mongo.go:313 installing mongodb-server
2014-05-05 14:45:34 INFO juju.utils.apt apt.go:128 Running: [apt-get --option=Dpkg::Options::=--force-confold --option=Dpkg::options::=--force-unsafe-io --assume-yes --quiet install --target-release precise-updates/cloud-tools mongodb-server]
2014-05-05 14:45:34 ERROR juju.utils.apt apt.go:134 apt-get command failed: exit status 100
args: []string{"apt-get", "--option=Dpkg::Options::=--force-confold", "--option=Dpkg::options::=--force-unsafe-io", "--assume-yes", "--quiet", "install", "--target-release", "precise-updates/cloud-tools", "mongodb-server"}
Reading package lists...
E: The value 'precise-updates/cloud-tools' is invalid for APT::Default-Release as such a release is not available in the sources
2014-05-05 14:45:34 ERROR juju.cmd supercommand.go:304 cannot install mongod: apt-get failed: exit status 100
Bootstrap failed, destroying environment
ERROR exit status 1
This error implies that cloud-init tried to install mongodb-server before cloud-tools was added to apt sources and update was called.