launchpad.net/~rogpeppe/juju-core/500-errgo-fix@v0.0.0-20140213181702-000000002356/doc/simplestreams-metadata.txt

Introduction
============

When Juju bootstraps, it needs two critical pieces of information:
1. The uuid of the image to use when starting new compute instances
2. The URL from which to download the correct version of a tools tarball

The necessary information is stored in a json metadata format called simplestreams.
The simplestreams format is used to describe related items in a structural fashion.
See the Launchpad project lp:simplestreams for more details.

For supported public clouds like Amazon, HP Cloud etc, no action is required by the
end user so the following information is more for those interested in what happens
under the covers. Those setting up a private cloud, or who want to change how things
work (eg use a different Ubuntu image), need to pay closer attention.

Basic Workflow
==============

Whether images or tools, Juju uses a search path to try and find suitable metadata.
The path components (in order of lookup) are:

1. User supplied location (specified by tools-metadata-url or image-metadata-url config settings)
2. The environment's cloud storage
3. Provider specific locations (eg keystone endpoint if on Openstack)
4. A web location with metadata for supported public clouds (https://streams.canonical.com)

Metadata may be inline signed, or unsigned. We indicate a metadata file is signed by using
a '.sjson' extension. Each location in the path is first searched for signed metadata, and
if none is found, unsigned metadata is attempted before moving onto the next path location.

Juju ships with public keys used to validate the integrity of image and tools metadata obtained
from https://streams.canonical.com. So out of the box, Juju will "Just Work" with any supported
public cloud, using signed metadata. Setting up metadata for a private (eg Openstack) cloud requires
metadata to be generated using tools which ship with Juju (more below).

Image Metadata Contents
=======================

Image metadata uses a simplestreams content type of "image-ids".
The product id is formed as follows:
"com.ubuntu.cloud:server:<series_version>:<arch>"
eg
"com.ubuntu.cloud:server:13.10:amd64"

Non-released images (eg beta, daily etc) have product ids like:
"com.ubuntu.cloud.daily:server:13.10:amd64"

The metadata index and product files are required to be in the following directory tree
(relative to the URL associated with each path component):

<path_url>
  |-streams
      |-v1
         |-index.(s)json
         |-product-foo.(s)json
         |-product-bar.(s)json

The index file must be called "index.(s)json" (sjson for signed). The various product files are
named according to the Path values contained in the index file.

Tools Metadata Contents
=======================

Tools metadata uses a simplestreams content type of "content-download".
The product id is formed as follows:
"com.ubuntu.juju:<series_version>:<arch>"
eg
"com.ubuntu.juju:12.04:amd64"

The metadata index and product files are required to be in the following directory tree
(relative to the URL associated with each path component). In addition, tools tarballs
which Juju needs to download are also expected.

<path_url>
  |-streams
  |   |-v1
  |      |-index.(s)json
  |      |-product-foo.(s)json
  |      |-product-bar.(s)json
  |
  |-releases
      |-tools-abc.tar.gz
      |-tools-def.tar.gz
      |-tools-xyz.tar.gz

The index file must be called "index.(s)json" (sjson for signed). The product file and
tools tarball name(s) match whatever is in the index/product files.

Configuration
=============

For supported public clouds, no extra configuration is required; things work out-of-the-box.
However, for testing purposes, or for non-supported cloud deployments, Juju needs to know
where to find the tools and which image to run. Even for supported public clouds where all
required metadata is available, the user can put their own metadata in the search path to
override what is provided by the cloud.

1. User specified URLs

These are initially specified in the environments.yaml file (and then subsequently copied to the
jenv file when the environment is bootstrapped). For images, use "image-metadata-url"; for tools,
use "tools-metadata-url". The URLs can point to a world readable container/bucket in the cloud,
an address served by a http server, or even a shared directory accessible by all node instances
running in the cloud.

eg assume an Apache http server with base URL https://juju-metadata, providing access to
information at <base>/images and <base>/tools. The Juju environment yaml file could have
the following entries (one or both):

tools-metadata-url: https://juju-metadata/tools
image-metadata-url: https://juju-metadata/images

The required files in each location is as per the directory layout described earlier.
For a shared directory, use a URL of the form "file:///sharedpath".

2. Cloud storage

If no matching metadata is found in the user specified URL, environment's cloud storage is searched.
No user configuration is required here - all Juju environments are set up with cloud storage which is
used to store state information, charms etc. Cloud storage setup is provider dependent; for Amazon
and Openstack clouds, the storage is defined by the "control-bucket" value, for Azure, the
"storage-account-name" value is relevant.

The (optional) directory structure inside the cloud storage is as follows:

<cloud storage top level>
  |-tools
  |   |-streams
  |       |-v1
  |   |-releases
  |
  |-images
      |-streams
          |-v1

Of course, if only custom image metadata is required, the tools directory will not be required,
and vice versa.

As a sidebar, note that if juju bootstrap is run with the --upload-tools option, the tools and metadata
are placed according to the above structure. That's why the tools are then available for Juju to use.

3. Provider specific storage

Providers may allow additional locations to search for metadata and tools. For Openstack, keystone
endpoints may be created by the cloud administrator. These are defined as follows:

juju-tools      : the <path_url> value as described above in Tools Metadata Contents
product-streams : the <path_url> value as described above in Image Metadata Contents

4. Central web location (https://streams.canonical.com)

This is the default location used to search for image and tools metadata and is used if no matches
are found earlier in any of the above locations. No user configuration is required.

Deploying Private Clouds
========================

There are two main issues when deploying a private cloud:
1. Images ids will be specific to the cloud
2. Often, outside internet access is blocked

Issue 1 means that image id metadata needs to be generated and made available.
Issue 2 means that tools need to be mirrored locally to make them accessible.

Juju tools exist to help with generating and validating image and tools metadata.
For tools, it is often easiest to just mirror https://streams.canonical.com/tools.
However image metadata cannot be simply mirrored because the image ids are taken
from the cloud storage provider, so this need to be generated and validated using
the commands described below.

The available Juju metadata tools can be seen by using the help command:
  juju help metadata

The overall workflow is:
- generate image metadata
- copy image metadata to somewhere in the metadata search path
- optionally, mirror tools to somewhere in the metadata search path
- optionally, configure tools-metadata-url and/or image-metadata-url

1. Image metadata

Generate image metadata using
  juju metadata generate-image -d <metadata_dir>

As a minimum, the above command needs to know the image id to use and a directory in which to write the files.
Other required parameters like region, series, architecture etc are taken from the current Juju environment (or
an environment specified with the -e option). These parameters can also be overridden on the command line.

The image metadata command can be run multiple times with different regions, series, architecture, and
it will keep adding to the metadata files. Once all required image ids have been added, the index and product
json files can be uploaded to a location in the Juju metadata search path. As per the Configuration section,
this may be somewhere specified by the image-metadata-url setting or the cloud's storage etc.

Examples:
1. image-metadata-url
 - upload contents of <metadata_dir> to http://somelocation
 - set image-metadata-url to http://somelocation/images
2. Cloud storage
 - upload contents of <metadata_dir> directly to environment's cloud storage

To ensure that the image metadata has been generated and uploaded correctly, use the validation command to
ensure an image id can be discovered for a given scenario (region series, arch):
  juju metadata validate-images

If run without parameters, the validation command will take all required details from the current Juju
environment (or as specified by -e) and print the image id it would use to spin up an instance.
Alternatively, series, region, architecture etc can be specified on the command line to override values
in the environment config.

2. Tools metadata

Generally, tools and related metadata is mirrored from https://streams.canonical.com/tools. However,
it is possible to manually generate metadata for a custom built tools tarball using:
  juju generate-tools -d <tools_dir>

where the required tools tarballs are first placed in a directory <tools_dir>/tools/releases.
Then, the contents of <tools_dir> can be uploaded to a location in the Juju metadata search path.
As per the Configuration section, this may be somewhere specified by the tools-metadata-url setting or
the cloud's storage etc.

Examples:
1. tools-metadata-url
 - upload contents of <tools_dir> to http://somelocation
 - set tools-metadata-url to http://somelocation/tools
2. Cloud storage
 - upload contents of <tools_dir> directly to environment's cloud storage

As with image metadata, the validation command is used to ensure tools are available for Juju to use:
  juju metadata validate-tools

The same comments apply. Run the validation tool without parameters to use details from the Juju
environment, or override values as required on the command line. See juju help metadata validate-tools
for more details.