Propagate OpenStack Swift object metadata into Elasticsearch
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MANIFEST.in Swift metadata sync. Sep 16, 2016
README.md
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requirements.txt
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README.md

Swift metadata sync

Synchronize Swift metadata with an Elasticsearch index. The tool can be used through the swift-metadata-sync binary. The synchronization daemon needs to run on a Swift node that hosts a container database.

The daemon will attempt to ensure correct mappings for the fields it knows about (e.g. x-timestamp, last-modified, content-length, etag). However, if an incorrect mapping has already been created, the metadata will still be propagated, but may not be searchable (e.g. a range query against dates would not return expected results).

Usage

The bare minimum required is a configuration file. It must include a pointer to the Swift drives (devices), the status directory to use (status_dir), number of items to process at a time (items_chunk), and an array of container mappings.

Here is a sample configuration file:

{
	"devices": "/srv/node",
	"status_dir": "/tmp",
	"items_chunk": 1000,
	"containers": [
		{
			"account": "AUTH_swift",
			"container": "swift",
			"es_hosts": "192.168.22.1",
			"index": "stuff"
		}
	]
}

For each Swift Account/Container, an elasticsearch cluster (es_hosts) and index (index) must be specified. The hosts argument accepts multiple, comma-separated entries to specify numerous servers.

If an index is changed and a re-index is desired, changing a container mapping's index value will restart indexing from the first object in that container.

Design

The daemon walks the Swift container database present on the node. The database rows contain the names of the objects and their status (notably last modified date and whether the object has been deleted). When an object's metadata is mutated, as long as fast-POST is enabled, a new row will be inserted in the database and the prior entry removed. This allows the daemon to continually walk the databases rows forward.

The advantage of this approach is that we never have to scan the entire database. The daemons must run on each of the container nodes to ensure that metadata is propagated, even if some of the container nodes fail.

There is no coordination mechanism between the processes walking the database, but each one attempts to only process a fraction of the entries and then verifies that all entries have been propagated.

After a failure, a daemon can be safely replaced with another node. It will only be doing bulk queries against Elasticsearch to verify that the changes it expects to have observed have been made. Once it catches up, it will resume operation from where the failure occurred.

The daemons also record the database ID. If a drive fails and the database has to replicated from another Swift node, the daemon will also restart from the beginning. This ensures correctness, but means that updates may not propagate as quickly after drive failures.

Testing it out

You can build a docker container with a Swift all-in-one and elasticsearch to try out metadata search. The container is defined in test/container. To build it, run: docker build -t metadata-sync test/container (this will tag the docker image as metadata-sync). Once the container is built, you can launch it as follows (assuming you're in the root directory of the swift-metadata-sync repository): docker run -P -d -v `pwd`:/swift-metadata-sync metadata-sync.

This will create a container running in the background (-d) with three ports exposed (-P), which maps the code tree into the container at /swift-metadata-sync. swift is listening on port 8080 inside the container and elasticsearch is on 9200. To check the port mappings, use: docker port <container-name>.

Once the container is running, you can use the Swift cluster as expected. The default mappings are configured in test/container/swift-metadata-sync.json. If you create the es-test container and an index named es-test, you should see the objects' metadata appear in elasticsearch.