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Plugin that makes it easy to load, dump, and sync data between Wukong and various data stores

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README.md

Wukong-Load

This Wukong plugin makes it easy to load data from the command-line into and out of various data stores.

It is assumed that you will independently deploy and configure each data store yourself (but see Ironfan).

Installation & Setup

Wukong-Load can be installed as a RubyGem:

$ sudo gem install wukong-load

Usage

wu-load

Wukong-Load provides a command-line program wu-load you can use to load data fed in over STDIN into a data store. It's designed to work effectively with wu-local and wu-dump as part of UNIX pipelines.

Get help on wu-load by running

$ wu-load --help

All input to wu-load should consist of newline-separated records over STDIN. For some data stores, JSON-formatted, Hash-like input is expected. Keys in the record may be interpreted as metadata about the record or about how to route the record within the data store.

Here are some quick examples which do what you think they do:

$ echo 'an arbitrary line of text' | wu-load kafka --topic=foo

$ echo '{"this": "record", "will": { "be": "indexed"}} | wu-load elasticsearch --index=foo --es_type=bar
$ echo '{"this": "record", "will": { "be": "updated"}, "_id": "existing_id"}' | wu-load elasticsearch --index=foo --es_type=bar

$ echo '{"this": "record", "will": { "be": "indexed"}} | wu-load mongodb --database=foo --collection=bar
$ echo '{"this": "record", "will": { "be": "upserted"}, "_id": "existing_id"}' | wu-load mongodb --database=foo --collection=bar

$ echo '{"this": "record", "is": "indexed"} | wu-load sql --database=foo --table=bar
$ echo '{"this": "record", "is": "upserted"}, "_id": "existing_id"}' | wu-load sql --database=foo --table=bar

Further details and options will depend on the data store you're writing to. See more information on each specific data store below. You can also get help for a specific data store with:

$ wu-load STORE_TYPE --help

Note: The wu-load program is not designed to handle any significant scale of data. It is only intended as a convenience tool for modeling how Wukong dataflows (which can scale) will interact with data stores.

wu-sync

Wukong-Load also provides a program wu-sync which can be used to sync data between filesystem like data stores.

wu-sync itself provides several types of syncs that can be chained together to create transactional, scalable processing for batch files.

Here's an example which syncs data from an FTP server to S3, providing a per-file transactional guarantee throughout:

$ wu-sync ftp --host=ftp.example.com --path=/remote/data --output=/data/incoming
$ wu-sync prepare --input=/data/incoming --output=/data/received
$ wu-sync prepare --input=/data/incoming --output=/data/received
$ wu-sync s3 --input=/data/received --bucket=s3://example.com/data

Further details and options will depend on the type of sync being performed. See more information on each specific sync below. You can also get help for a specific sync with:

$ wu-sync SYNC_TYPE --help

Kafka Usage

Kafka uses the concept of "topics" which contain numbered "partitions" that contain a sequence of events concatenated together. Producers (writers) to Kafka dump in events and consumers (readers) request data between particular byte offsets on particular partitions of particular topics. Kafka's data model is very simple (everything is a sequence of bytes) so it can store any kind of data.

Get options for loading data from or dumping data to Kafka:

$ wu-load kafka --help
$ wu-dump kafka --help

Connecting

wu-load and wu-dump try to connect to a Kafka broker at a default host (localhost) and a port (9092). You can change this:

$ cat data.txt | wu-load kafka --host=10.122.123.124 --port=1234
$ wu-dump kafka --host=10.122.123.124 --port=1234

Routing

wu-load and wu-dump both assume a default topic (wukong) and partition (0), but you can change these:

$ cat data.txt | wu-load kafka --topic=messages --partition=6
$ wu-dump kafka --topic=messages --partition=6

Producing

Writing data to Kafka is simple: pick a topic and partition and push in some bytes:

$ cat data.txt | wu-load kafka --topic=messages

To achieve higher throughput (though, remember, wu-dump and wu-load are not designed for significant load), set the --batch_size option up a bit:

$ cat data.txt | wu-load kafka --topic=messages --batch_size=1000

Consuming

Consuming data from Kafka requires picking a topic, partition, and a byte-offset.

It's rare to want to choose a specific byte-offset (typically only occurs in delicate situations that no one wants to be in) but you can do it easily:

$ wu-dump kafka --topic=foo --offset=65536

The usual approach is to consume either from the beginning or end of available data on a topic & partition. wu-dump's default behavior is to start from the end of a topic:

$ wu-dump kafka --topic=foo

but you can also start from the beginning:

$ wu-dump kafka --topic=foo --from_beginning

Another common pattern among Kafka consumers is to choose an offset that is "wherever you last left off". Kafka does not provide a mechansim to remember per-consumer last-offsets so it's up to consumers to do this for themselves. Since wu-dump is not designed to run continuously, it does not store "wherever you last left off".

Elasticsearch Usage

Note:: ElasticSearch support for wu-dump is not currently implemented.

ElasticSearch uses the concept of "indices" which contain "types" to store "documents", each of which is a schema-less, Hash-like structure. Every document must also have an ID which can be generated by ElasticSearch at index (write) time.

wu-load, like many tools that interact with ElasticSearch, uses JSON-serialization. See full options with

$ wu-load elasticsearch --help

Connecting

wu-load tries to connect to an Elasticsearch server at a default host (localhost) and port (9200). You can change these:

$ cat data.json | wu-load elasticsearch --host=10.122.123.124 --port=80

Routing

wu-load loads each document into default index (wukong) and type (streaming_record), but you can change these:

$ cat data.json | wu-load elasticsearch --index=publication --es_type=book

A record with an _index or _type field will override these default settings. You can change the names of the fields used with the --index_field and --es_type_field options:

$ cat data.json | wu-load elasticsearch --index=industry --es_type=publication --index_field=publisher --es_type_field=classification

Creates vs. Updates

If an input record contains a value for the field _id then that value will be as the ID of the document when written, possibly overwriting a document that already exists -- an update.

You can change the field you use for the Elasticsearch ID property:

$ cat data.json | wu-load elasticsearch --index=media --es_type=books --id_field="ISBN"

MongoDB Usage

Note:: MongoDB support for wu-dump is not currently implemented.

MongoDB uses the concept of "databases" which contain "collections" to store "documents", each of which is a schema-less, Hash-like structure. Every document must also have an ID which can be generated by MongoDB at insert (write) time.

wu-load, like many tools that interact with MongoDB, uses JSON-serialization. See full options with

$ wu-load mongodb --help

Connecting

wu-load tries to connect to an MongoDB server at a default host (localhost) and port (27017). You can change these:

$ cat data.json | wu-load mongodb --host=10.122.123.124 --port=1234

Routing

wu-load loads each document into default database (wukong) and collection (streaming_record), but you can change these:

$ cat data.json | wu-load mongodb --database=publication --collection=book

A record with a _database or _collection field will override these default settings. You can change the names of the fields used with the --database_field and --collection_field options:

$ cat data.json | wu-load mongodb --database=industry --collection=publication --database_field=publisher --collection_field=classification

Creates vs. Updates

If an input record contains a value for the field _id then that value will be as the ID of the document when written, possibly overwriting a document that already exists -- an update.

You can change the field you use for the MongoDB ID property:

$ cat data.json | wu-load mongodb --database=publication --collection=books --id_field="ISBN"

Syncing

Syncing data between filesystems is always challenging to do well though there are many good tools available.

In a Big Data setting, syncs are even more challenging because of the size of the files involved which exacerbates problems of blocking, atomicity, transactionality, throughput, memory, &c. The best approach is to split the process up into several steps, each of which does one simple operation robustly, correctly, and in a way that can be tracked.

The wu-sync provides several types of syncs that can be used together to create transactional, scalable processing for batch files. Each wu-sync command is meant to be run on a regular schedule every few minutes, perhaps via cron.

All of the wu-sync sync types accept the --dry_run option which will go through the sync showing what would be done but not doing it.

From FTP

The ftp sync will sync data from an FTP server to a local disk. It supports several different flavors of FTP, including FTPS and SFTP.

On each invocation, wu-sync ftp will download any files (or parts of files) present under --path on the remote server but not present in the local --output directory. Files present on the local filesystem but not on the remote server will be ignored.

The lftp program is required for wu-ftp to function.

Get general help on wu-sync ftp with

$ wu-sync ftp --help

Note: Since FTP is conceptually "single-threaded", no throughput gains are achieved by having multiple processes try and read the same file on the same FTP server. For this reason, wu-sync ftp can be used in a production setting, acting as the fundamental building block of a more distributed system of which each wu-sync ftp process is responsible for some files on some FTP servers.

Specifying FTP protocol, host, and credentials

By default, wu-sync ftp will try to connect anonymously to an FTP server running on the local machine. The --protocol, --host, --port, --username, and --password options can be used to configure this behavior. Here's an example of connecting to a remote FTP server using a secure FTPS connection:

$ wu-sync ftp --host=ftp.example.com --protocol=ftps --username=bob --password=<password> --output=/data/ftp

You can use the FTP_PASSWORD environment variable if you don't want to pass the password on the command-line.

The port is determined automatically from the protocol (e.g. - 21 for ftp, 22 for sftp, 443 for ftps) but can be explicitly given with the --port flag.

Preparing Files for Downstream Consumption

One of the immediate issues that arises when syncing files is that it may not be clear to a client when the file on the remote server the client is connected to has finished uploading. It may also not be clear if the file has finished downloading to the local filesystem.

The approach taken by Wukong is to run a separate "archival" step which syncs data in a local --input directory with data in a local --output directory. Files will only show up in the --output directory when they are complete, as measured by them having stopped growing in the --input directory.

wu-sync is not a continuously running process, however, and so the only way for it to reliably know when files have stopped growing is for it to store file sizes from one invocation in order to compare them to file sizes on the next invocation. For this reason, creating files in the --output directory requires at at least two invocations of wu-sync (with the same set of parameters).

Here's an example of the --input directory /data/ftp:

/data/ftp
├──   alice
│   └──   project_1
│       └──   file_1
├──   bob
│   ├──   project_1
│   │   ├──   file_1
│   │   ├──   file_2
│   │   └──   file_3
│   └──   project_2
│       ├──   file_1
│       └──   file_2
└──   README

After running wu-sync prepare twice

$ wu-sync prepare --input=/data/ftp --output=/data/clean
$ wu-sync prepare --input=/data/ftp --output=/data/clean

the --output directory /data/clean should look exactly the same as the input directory:

/data/clean
├──   alice
│   └──   project_1
│       └──   file_1
├──   bob
│   ├──   project_1
│   │   ├──   file_1
│   │   ├──   file_2
│   │   └──   file_3
│   └──   project_2
│       ├──   file_1
│       └──   file_2
└──   README

Nothing here seems magical, but the log output of wu-sync prepare reveals a lot that's going on to ensure that only complete files are processed.

Note: The files created in the --output directory are hardlinks pointing at the original files in the --input directory.

Splitting input files

The --split option will make wu-sync prepare split large files in the --input directory into many manageable, smaller files in the --output directory.

Assume that Alice has been busy and that the file /data/clean/alice/project_1/file_1 is big. After running wu-sync prepare twice:

$ wu-sync prepare --input=/data/ftp --output=/data/clean --split
$ wu-sync prepare --input=/data/ftp --output=/data/clean --split

the --output directory /data/clean will look like this:

/data/clean
├──   alice
│   └──   project_1
│       ├──   file_1.part-0000
│       ├──   file_1.part-0001
│       └──   file_1.part-0002
├──   bob
│   ├──   project_1
│   │   ├──   file_1.part-0000
│   │   ├──   file_2.part-0000
│   │   └──   file_3.part-0000
│   └──   project_2
│       ├──   file_1.part-0000
│       └──   file_2.part-0000
└──   README.part-0000

Alice's big --input file has been split into three --output files. Bob's --input files were smaller than the split size so they each resulted in a single --output file.

You can change the number of lines in each file split with the --lines option and switch to splitting by bytes with the --bytes option.

Note: When splitting, the files in the --output directory are real files instead of hardlinks as they are by default.

Ordering output files

Some tools require their input to be ordered and for these tools wu-sync prepare provides an --ordered option which will reorganize files in the --output directory so that they are totally ordered:

$ wu-sync prepare --input=/data/ftp --output=/data/clean --ordered
$ wu-sync prepare --input=/data/ftp --output=/data/clean --ordered

This would result in the following structure for the --output directory:

/data/clean
├──   alice
│   └──   2013
│       └──   09
│           └──   20
│               └──   20130920-071142-1-alice-project_1-file_1
├──   bob
│   └──   2013
│       └──   09
│           └──   20
│               ├──   20130920-071142-2-bob-project_1-file_1
│               ├──   20130920-071142-3-bob-project_1-file_2
│               ├──   20130920-071142-4-bob-project_1-file_3
│               ├──   20130920-071142-5-bob-project_2-file_1
│               └──   20130920-071142-6-bob-project_2-file_2
└──   root
    └──   2013
        └──   09
            └──   20
                └──   20130920-071142-0-README

The ordering is built up from:

  1. Each top-level subdirectory of the --input directory appears in the root of the --output directory. (Files that were in the --input directory itself are put in the root subdirectory of the --output directory.)

  2. Within each top-level subdirectory, a daily directory is created based on the time the corresponding --input file was recognized as completed.

  3. All files within the top-level subdirectory of the --input directory are placed within this daily directory with basenames constructed from

    a. the time the corresponding --input file was recognized as completed b. an incrementing counter c. the path of the --input file relative to the --input directory

The --ordered option can be combined with the --split option:

$ wu-sync prepare --input=/data/ftp --output=/data/clean --ordered
$ wu-sync prepare --input=/data/ftp --output=/data/clean --ordered

to get

/data/clean
├──   alice
│   └──   2013
│       └──   09
│           └──   20
│               ├──   20130920-071643-1-alice-project_1-file_1.part-0000
│               ├──   20130920-071643-1-alice-project_1-file_1.part-0001
│               └──   20130920-071643-1-alice-project_1-file_1.part-0002
├──   bob
│   └──   2013
│       └──   09
│           └──   20
│               ├──   20130920-071643-2-bob-project_1-file_1.part-0000
│               ├──   20130920-071643-3-bob-project_1-file_2.part-0000
│               ├──   20130920-071643-4-bob-project_1-file_3.part-0000
│               ├──   20130920-071643-5-bob-project_2-file_1.part-0000
│               └──   20130920-071643-6-bob-project_2-file_2.part-0000
└──   root
    └──   2013
        └──   09
            └──   20
                └──   20130920-071643-0-README.part-0000

Including metadata

The --metadata option produces a JSON-formatted metadata file for each data file produced in the --output directory.

Metadata files are stored in a separate hierarchy in the --output directory from the data files. Within this separate hierarchy they have the same relative path as their corresponding data files, but with an extra suffix of .meta. Here's an example:

$ wu-sync prepare --input=/data/ftp --output=/data/clean --metadata
$ wu-sync prepare --input=/data/ftp --output=/data/clean --metadata

which produces

/data/clean
├──   alice
│   └──   2013
│       └──   09
│           └──   20
│               └──   20130920-072539-1-alice-project_1-file_1
├──   alice_meta
│   └──   2013
│       └──   09
│           └──   20
│               └──   20130920-072539-1-alice-project_1-file_1.meta
├──   bob
│   └──   2013
│       └──   09
│           └──   20
│               ├──   20130920-072539-2-bob-project_1-file_1
│               ├──   20130920-072539-3-bob-project_1-file_2
│               ├──   20130920-072539-4-bob-project_1-file_3
│               ├──   20130920-072539-5-bob-project_2-file_1
│               └──   20130920-072539-6-bob-project_2-file_2
├──   bob_meta
│   └──   2013
│       └──   09
│           └──   20
│               ├──   20130920-072539-2-bob-project_1-file_1.meta
│               ├──   20130920-072539-3-bob-project_1-file_2.meta
│               ├──   20130920-072539-4-bob-project_1-file_3.meta
│               ├──   20130920-072539-5-bob-project_2-file_1.meta
│               └──   20130920-072539-6-bob-project_2-file_2.meta
├──   root
│   └──   2013
│       └──   09
│           └──   20
│               └──   20130920-072539-0-README
└──   root_meta
    └──   2013
        └──   09
            └──   20
                └──   20130920-072539-0-README.meta

Notice that the --metadata option implies the --ordered option. This is so metadata files are guaranteed to come later than their corresponding data file in any lexicographically ordered walking of the --output directory.

This is so that syncing tools will transfer a metadata file after they transfer its corresponding data file. Since metadata files are also small, this means that downstream tools can use the presence or absence of a metadata file to know for sure whether a data file has already been transferred completely -- they won't have to do the dance that wu-sync prepare is doing.

The content of a metadata file is very simple. Here's /data/clean/alice_meta/2013/09/20/20130920-072539-1-alice-project_1-file_1.meta:

{
  "path": "alice/2013/09/20/20130920-072539-1-alice-project_1-file_1",
  "meta_path": "alice_meta/2013/09/20/20130920-072539-1-alice-project_1-file_1.meta",
  "size": 168894,
  "md5": "0a61f0919f546ce04fc119b028b88a2e"
}

Both path and meta_path are relative to the --output directory.

The --metadata option can also be combined with the --split option.

Multiple Output Directories

Using multiple --output directories mounted on different devices can greatly speed up operation as large files are read & written. When using multiple --output directories, each consecutively processed file in the --input directory will be assigned one of the output directories in a round-robin fashion:

$ wu-sync prepare --input=/data/ftp --output=/data/clean_1,/data/clean_2
$ wu-sync prepare --input=/data/ftp --output=/data/clean_1,/data/clean_2

To S3

The s3 sync will sync data from a local --input directory to an S3 --bucket and path. It requires the s3cmd program.

Here's an example.

$ wu-sync s3 --input=/data/clean --bucket=s3://example.com/archive

This example assumes that the underlying s3cmd has been installed with appropriate credentials to write to the s3://example.com bucket (or that the bucket s3://example.com is world-writable). If not, an s3cmd configuration file can be passed in with the --s3cmd_config file:

$ wu-sync s3 --input=/data/clean --bucket=s3://example.com/archive --s3cmd_config=config/s3cfg

The wu-sync s3 command also works with multiple --input directories. This is to work nicely with the wu-sync prepare command which has multiple --output directories:

$ wu-sync s3 --input=/data/clean_1,/data/clean_2 --bucket=s3://example.com/archive --s3cmd_config=config/s3cfg

Working with multiple data sources

Note: This functionality is designed to work in the context of a deploy pack only.

Syncing several FTP sources is possibly with wu-sync but it's a lot to type. The wu-sync-all command can read a configuration file with pre-defined data sources and run each of the sync types on each of the sources (or just some of them).

Within one of the configuration files in your deploy pack (either config/settings.yml or an environment-specific config/environments/ENVIRONMENT.yml) create a listener for each of your souces as follows:

---
listeners:
  nasa:
    ftp:
      host:     ftp.nasa.gov
      username: narmstrong
      password: first!
      path:     /data/latest
    prepare:
      ordered:  true
      metadata: true
    s3:
      bucket: s3://archive.example.com/nasa
  usaf:
    ftp:
      host:     ftp.usaf.gov
      username: bobross
      password: xxx
      path:     /data/latest
    prepare:
      split: true
      lines: 1_000_000
    s3:
      bucket: s3://archive.example.com/usaf
  ...

The top-level keys in the listeners Hash (nasa, usaf, &c.) are each the name of a data source. The next-level keys (ftp, prepare, s3) each name a sync type and give the options for that type. These options are exactly the same as the usual options for that sync-type. Options not supplied via the configuration file (typically "system" parameters like --input and --output directories) are expected to be supplied on the command-line at runtime.

With a proper configuration with valid listeners, the following commands will perform a sync from FTP to S3 of all data sources:

$ wu-sync-all ftp --output=/data/incoming
$ wu-sync-all prepare --input=/data/incoming --output=/data/received
$ wu-sync-all prepare --input=/data/incoming --output=/data/received
$ wu-sync-all s3 --input=/data/received

The --only and --except options can be used to limit wu-sync-all's action to a desired subset of sources:

$ wu-sync-all ftp --output=/data/incoming --only=nasa,usaf
$ wu-sync-all ftp --output=/data/incoming --except=wto
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