An implementation of Amazon's DynamoDB, focussed on correctness and performance, and built on LevelDB (well, @rvagg's awesome LevelUP to be precise).
This project aims to match the live DynamoDB instances as closely as possible (and is tested against them in various regions), including all limits and error messages.
If you've been using v1.x or v0.x or with a saved path on your filesystem, you
should note that key schema may have changed with the move from
level-sublevel
to subleveldown
. The safest way to deal with this is to
export your DB to JSON using Scans, then upgrade and import with BatchWrites
into the new version.
Good question! These days it's actually pretty good, and considering it's now probably used by countless AWS devs, it'll probably be well supported going forward. Unless you specifically can't, or don't want to, use Java, or you're having problems with it, you'll probably be better off sticking with it! Originally, however, DynamoDB Local didn't exist, and when it did, differed a lot from the live instances in ways that caused my company issues. Most of those issues have been addressed in time, but DynamoDB Local does still differ in a number of ways from the live DynamoDB instances โ (see below) for details.
$ dynalite --help
Usage: dynalite [--port <port>] [--path <path>] [options]
A DynamoDB http server, optionally backed by LevelDB
Options:
--help Display this help message and exit
--port <port> The port to listen on (default: 4567)
--path <path> The path to use for the LevelDB store (in-memory by default)
--ssl Enable SSL for the web server (default: false)
--createTableMs <ms> Amount of time tables stay in CREATING state (default: 500)
--deleteTableMs <ms> Amount of time tables stay in DELETING state (default: 500)
--updateTableMs <ms> Amount of time tables stay in UPDATING state (default: 500)
--maxItemSizeKb <kb> Maximum item size (default: 400)
Report bugs at github.com/mhart/dynalite/issues
Or programmatically:
// Returns a standard Node.js HTTP server
var dynalite = require('dynalite'),
dynaliteServer = dynalite({path: './mydb', createTableMs: 50})
// Listen on port 4567
dynaliteServer.listen(4567, function(err) {
if (err) throw err
console.log('Dynalite started on port 4567')
})
Once running, here's how you use the AWS SDK to connect (after configuring the SDK):
var AWS = require('aws-sdk')
var dynamo = new AWS.DynamoDB({endpoint: 'http://localhost:4567'})
dynamo.listTables(console.log.bind(console))
With npm do:
$ npm install -g dynalite
- Implement DynamoDB Streams
- Implement
ReturnItemCollectionMetrics
on all remaining endpoints - Implement size info for tables and indexes
- Add ProvisionedThroughput checking
- See open issues on GitHub for any further TODOs
Part of the reason I wrote dynalite was due to the existing mock libraries not exhibiting the same behaviour as the live instances. Amazon then released their DynamoDB Local Java, but the early versions were still very different. The latest version I checked (2016-04-19) is much better, but still has a few differences.
Some of these are documented, but most aren't - the items below are a rough list of the issues found, vaguely in order of importance:
- Does not return nested attributes correctly for
UpdateItem
- Does not calculate size limits accurately for
BatchGetItem
/Query
/Scan
result sets - Does deal with
ALL_ATTRIBUTES
correctly for global index onQuery
/Scan
- Does not prevent primary keys in
QueryFilter
andFilterExpression
forQuery
- Does not detect duplicate values in
AttributesToGet
- Does not return
LastEvaluatedKey
when size just over limit forQuery
/Scan
- Does not return
ConsistentRead
property inUnprocessedKeys
inBatchGetItem
even if requested - Doesn't return
ConsumedCapacity
(documented - but makes it very hard to calculate expected usage) - Often returns 500 instead of 400 (or similarly appropriate status)
- Different serialization and validation error messages from live instances (makes it hard to debug)
- Does not return
application/json
ifapplication/json
is requested - Does not return
Query
/Scan
items in same order when using hash key or hashGlobalSecondaryIndex
(shouldn't rely on this anyway)