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microcosm-resourcesync

Synchronize resources between endpoints

In non-trivial deployments of RESTful services, it is common to have multiple copies of the same service running in different environments (development, testing, staging, production, etc). In many cases, it is useful to synchronize some resource data between environments by first copying content to an intermediate format and then copying that format to another environment.

This process is especially useful if the intermediate format lives in version control and supports diffs and merging well.

Installation

Install into a virtualenv:

mkvirtualenv microcosm-resourcesync --python=python3
pip install -e .

Using libyaml

YAML performance is significantly better using libyaml. On OSX:

brew install yaml-cpp libyaml
pip uninstall PyYAML
# installing with pip appears not to work
python -m easy_install pyyaml

Usage

The main usage is synchronizes from one or more origin endpoint to a destination endpoint:

resource-sync [OPTIONS] [ORIGIN]... DESTINATION

Where endpoints may be any of the following:

  • An HTTP(S) URL
  • A YAML file
  • A directory path
  • The literal - (for stdin/stdout)

Assumptions

Resources are assumed to adhere to certain REST conventions:

  • Resources are formatted as either JSON or YAML;

    Origin endpoints define their own format whereas destination endpoints define a default format; the latter can be overridden on the command line using --json or --yaml.

    Additional formatters can be added with code changes.

  • Resources define a few well-known attributes, including id, type, and uri.

    These attributes are derived from the parsed resource dictionary using a schema.

    The default behavior uses a schema based on the HAL JSON spec and includes additional processing for hypertext (HATEOAS).

    An alternate, simple schema can also be selected using --simple (vs --hal).

  • Resources can be managed remotely over HTTP(S) using GET or PUT on the uri.

    Both operations are assumed to be idempotent. PUT operations will be retried a limited number of times in the event of connection-related errors.

Capturing Data

A common use case is pull data from an HTTP endpoint to a local directory:

resource-sync https://example.com/foo /path/to/local/data

The HTTP response may contain multiple resources (especially for endpoints implementing the microcosm Search convention or some other form of pagination). Similarly, the --follow-xxx flags can be used to control how resource-sync traverses hypertext ("links") present in the HTTP response and pulls further resources.

Each resource captured from the HTTP endpoint will be saved into its own file within the directory tree, using type-specific sub-directories. By default, each resource will be stored as YAML (for better human readability), though JSON may be used instead via the --json flag.

Replaying Data

Another common use case is push data from a local directory to an HTTP endpoint:

resource-sync /path/to/local/data https://example.com

In this case, resource-sync will push the local resource(s) to the remote server.

If the resources define dependency relationships, a topological sort will be used to ensure that resources are pushed in the correct order (e.g. assuming a remote server with no prior content).

Missing Features

  • The --rm flag has no effect for directory trees or HTTP(S) endpoints.

    This means that there is currently now way to propage a removal from an origin to a destination, although a crude approximation can be achieved for a version-controlled directory by first removing all YAML/JSON files from the tree and then re-running the sychronization. The version control system should detect any files that were not restored by the re-run.

  • The HTTP(S) endpoints should support batching to speed up writes.

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Synchronize resources between endpoints

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