Juju bootstrap attempts to use the architecture of the host to select tools for the target environment even though constraints instruct it to do otherwise.
ubuntu@winton-02:~$ juju bootstrap -v --constraints="arch=amd64"
verbose is deprecated with the current meaning, use show-log
2014-02-21 03:57:15 INFO juju.environs open.go:158 environment info already exists; using New not Prepare
2014-02-21 03:57:15 INFO juju.provider.ec2 ec2.go:200 opening environment "us-west-1"
2014-02-21 03:57:21 INFO juju.environs.bootstrap bootstrap.go:46 bootstrapping environment "us-west-1"
2014-02-21 03:57:28 INFO juju.environs.tools tools.go:85 reading tools with major.minor version 1.17
2014-02-21 03:57:28 INFO juju.environs.tools tools.go:96 filtering tools by series: precise
2014-02-21 03:57:28 INFO juju.environs.tools tools.go:99 filtering tools by architecture: amd64
2014-02-21 03:57:33 WARNING juju.environs.bootstrap synctools.go:108 no tools available, attempting to retrieve from https://streams.canonical.com/juju/tools
2014-02-21 03:57:33 INFO juju.environs.sync sync.go:142 using sync tools source: https://streams.canonical.com/juju/tools
2014-02-21 03:57:33 INFO juju.environs.sync sync.go:65 listing available tools
2014-02-21 03:57:33 WARNING juju.environs.bootstrap synctools.go:42 no tools found, so attempting to build and upload new tools
2014-02-21 03:57:33 INFO juju.environs.tools build.go:162 found existing jujud
2014-02-21 03:57:33 INFO juju.environs.tools build.go:172 target: /tmp/juju-tools917941044/jujud
2014-02-21 03:57:38 INFO juju.environs.sync sync.go:218 built tools 1.17.3.1-trusty-ppc64 (6090kB)
2014-02-21 03:57:38 INFO juju.environs.tools simplestreams.go:357 Writing tools/streams/v1/index.json
2014-02-21 03:57:38 INFO juju.environs.tools simplestreams.go:357 Writing tools/streams/v1/com.ubuntu.juju:released:tools.json
2014-02-21 03:57:38 INFO juju.environs.sync sync.go:142 using sync tools source: file:///tmp/214616323/tools
2014-02-21 03:57:38 INFO juju.environs.sync sync.go:65 listing available tools
2014-02-21 03:57:38 INFO juju.environs.sync sync.go:86 found 2 tools
2014-02-21 03:57:38 INFO juju.environs.sync sync.go:96 listing target tools storage
2014-02-21 03:57:41 INFO juju.environs.sync sync.go:109 found 2 tools in target; 0 tools to be copied
2014-02-21 03:57:41 INFO juju.environs.sync sync.go:114 copied 0 tools
2014-02-21 03:57:41 INFO juju.environs.sync sync.go:116 generating tools metadata
2014-02-21 03:57:44 INFO juju.environs.tools simplestreams.go:357 Writing tools/streams/v1/index.json
2014-02-21 03:57:45 INFO juju.environs.tools simplestreams.go:357 Writing tools/streams/v1/com.ubuntu.juju:released:tools.json
2014-02-21 03:57:46 INFO juju.environs.sync sync.go:128 tools metadata written
2014-02-21 03:57:46 INFO juju.environs.tools tools.go:85 reading tools with major.minor version 1.17
2014-02-21 03:57:46 INFO juju.environs.tools tools.go:96 filtering tools by series: precise
2014-02-21 03:57:46 INFO juju.environs.tools tools.go:99 filtering tools by architecture: amd64
2014-02-21 03:57:48 ERROR juju.provider.common bootstrap.go:140 bootstrap failed: cannot find bootstrap tools: no tools available
2014-02-21 03:57:48 ERROR juju.cmd supercommand.go:293 cannot find bootstrap tools: no tools available