monstache

monstache

a go daemon which syncs mongodb to elasticsearch in near realtime

Install

You can download monstache binaries for Linux from the Releases page.

Or you can build monstache from source using go get

go get github.com/rwynn/monstache

Getting Started

Since monstache uses the mongodb oplog to tail events it is required that mongodb is configured to produce an oplog.

This can be ensured by doing one of the following:

• Setting up replica sets

• Passing --master to the mongod process

• Setting the following in /etc/mongod.conf

  master = true
  

You will also want to ensure that automatic index creation is not disabled in elasticsearch.yml.

monstache is not bi-directional. It only syncs from mongodb to elasticsearch.

Usage

monstache [-f PATH-TO-TOML] [options]

All command line arguments are optional. With no arguments monstache expects to connect to mongodb and elasticsearch on localhost using the default ports.

If the -f option is supplied the argument value should be the file path of a TOML config file.

A sample TOML config file looks like this:

mongo-url = "mongodb://someuser:password@localhost:40001"
mongo-pem-file = "/path/to/mongoCert.pem"
elasticsearch-url = "http://someuser:password@localhost:9200"
elasticsearch-max-conns = 10
replay = false
resume = true
resume-name = "default"
namespace-regex = "^mydb.mycollection$"
namespace-exclude-regex = "^mydb.ignorecollection$"
gtm-channel-size = 200
index-files = true
file-highlighting = true
file-namespaces = ["users.fs.files"]
verbose = true

All options in the config file above also work if passed explicity by the same name to the monstache command

Arguments supplied on the command line override settings in a config file

The following defaults are used for missing config values:

mongo-url -> localhost
mongo-pem-file -> nil
elasticsearch-url -> localhost
elasticsearch-max-conns -> 10
elasticsearch-retry-seconds -> 0 
elasticsearch-max-docs -> 100
elasticsearch-max-bytes -> 16384
elasticsearch-max-seconds -> 5
replay -> false
resume -> false
resume-name -> default
namespace-regex -> nil
namespace-exclude-regex -> nil
gtm-channel-size -> 100
index-files -> false
file-highlighting -> false
file-namespaces -> nil
verbose -> false

When resume is true, monstache writes the timestamp of mongodb operations it has successfully synced to elasticsearch to the collection monstache.monstache. It also reads this value from that collection when it starts in order to replay events which it might have missed because monstache was stopped. monstache uses the value of resume-name as a key when storing and retrieving timestamps. If resume is true but resume-name is not supplied this key defaults to default.

When replay is true, monstache replays all events from the beginning of the mongodb oplog and syncs them to elasticsearch.

When resume and replay are both true, monstache replays all events from the beginning of the mongodb oplog, syncs them to elasticsearch and also writes the timestamp of processed events to monstache.monstache.

When neither resume nor replay are true, monstache reads the last timestamp in the oplog and starts listening for events occurring after this timestamp. Timestamps are not written to monstache.monstache. This is the default behavior.

When namespace-regex is given this regex is tested against the namespace, database.collection, of the event. If the regex matches monstache continues processing event filters, otherwise it drops the event. By default monstache processes events in all databases and all collections with the exception of the reserved database monstache, any collections suffixed with .chunks, and the system collections.

When namespace-exclude-regex is given this regex is tested against the namespace, database.collection, of the event. If the regex matches monstache ignores the event, otherwise it continues processing event filters. By default monstache processes events in all databases and all collections with the exception of the reserved database monstache, any collections suffixed with .chunks, and the system collections.

When gtm-channel-size is given it controls the size of the go channels created for processing events. When many events are processed at once a larger channel size may prevent blocking in gtm.

When mongo-pem-file is given monstache will use the given file path to add a local certificate to x509 cert pool when connecting to mongodb. This should only be used when mongodb is configured with SSL enabled.

When index-files is true monstache will index the raw content of files stored in GridFS into elasticsearch as an attachment type. By default index-files is false meaning that monstache will only index metadata associated with files stored in GridFS. In order for index-files to index the raw content of files stored in GridFS you must install a plugin for elasticsearch. For versions of elasticsearch prior to version 5, you should install the mapper-attachments plugin. In version 5 or greater of elasticsearch the mapper-attachment plugin is deprecated and you should install the ingest-attachment plugin instead. For further information on how to configure monstache to index content from grids, see the section Indexing Gridfs Files.

The file-namespaces config must be set when index-files is enabled. file-namespaces must be set to an array of mongodb namespace strings. Files uploaded through gridfs to any of the namespaces in file-namespaces will be retrieved and their raw content indexed into elasticsearch via either the mapper-attachments or ingest-attachment plugin.

When file-highlighting is true monstache will enable the ability to return highlighted keywords in the extracted text of files for queries on files which were indexed in elasticsearch from gridfs.

When verbose is true monstache with enable debug logging including a trace of requests to elasticsearch

When elasticseach-retry-seconds is greater than 0 a failed request to elasticsearch with retry the request after the given number of seconds

When elasticsearch-max-docs is given a bulk index request to elasticsearch will be forced when the buffer reaches the given number of documents

When elasticsearch-max-bytes is given a bulk index request to elasticsearch will be forced when the buffer reaches the given number of bytes

When elasticsearch-max-seconds is given a bulk index request to elasticsearch will be forced when a request has not been made in the given number of seconds

Config Syntax

For information on the syntax of the mongodb URL see Standard Connection String Format

The elasticsearch URL should point to where elasticsearch's RESTful API is configured

Document Mapping

When indexing documents from mongodb into elasticsearch the mapping is as follows:

mongodb database -> elasticsearch index
mongodb collection -> elasticsearch type
mongodb document id -> elasticsearch document id

If these default won't work for some reason you can override the index and collection mapping on a per collection basis by adding the following to your TOML config file:

[[mapping]]
namespace = "test.test"
index = "index1"
type = "type1"

[[mapping]]
namespace = "test.test2"
index = "index2"
type = "type2"

With the configuration above documents in the test.test namespace in mongodb are indexed into the index1 index in elasticsearch with the type1 type.

Make sure that automatic index creation is not disabled in elasticsearch.yml.

If automatic index creation must be controlled, whitelist any indexes in elasticsearch.yml that monstache will create.

Field Mapping

monstache uses the amazing otto library to provide transformation at the document field level in javascript. You can associate one javascript mapping function per mongodb collection. These javascript functions are added to your TOML config file, for example:

[[script]]
namespace = "mydb.mycollection"
script = """
var counter = 1;
module.exports = function(doc) {
	doc.foo += "test" + counter;
	counter++;
	return _.omit(doc, "password", "secret");
}
"""

[[script]]
namespace = "anotherdb.anothercollection"
script = """
var counter = 1;
module.exports = function(doc) {
	doc.foo += "test2" + counter;
	counter++;
	return doc;
}
"""

The example TOML above configures 2 scripts. The first is applied to mycollection in mydb while the second is applied to anothercollection in anotherdb.

You will notice that the multi-line string feature of TOML is used to assign a javascript snippet to the variable named script. The javascript assigned to script must assign a function to the exports property of the module object. This function will be passed the document from mongodb just before it is indexed in elasticsearch. Inside the function you can manipulate the document to drop fields, add fields, or augment the existing fields. The only requirement is that you return an object. The object returned from the mapping function is what actually gets indexed in elasticsearch. The this reference in the mapping function is assigned to the document from mongodb.

You may have noticed that in the example above the exported mapping function closes over a var named counter. You can use closures to maintain state between invocations of your mapping function.

Finally, since Otto makes it so easy, the venerable Underscore library is included for you at no extra charge. Feel free to abuse the power of the _.

Indexing GridFS Files

As of version 1.1 monstache supports indexing the raw content of files stored in GridFS into elasticsearch for full text search. This feature requires that you install an elasticsearch plugin which enables the field type attachment. For versions of elasticsearch prior to version 5 you should install the mapper-attachments plugin. For version 5 or later of elasticsearch you should instead install the ingest-attachment plugin.

Once you have installed the appropriate plugin for elasticsearch, getting file content from GridFS into elasticsearch is as simple as configuring monstache. You will want to enable the index-files option and also tell monstache the namespace of all collections which will hold GridFS files. For example in your TOML config file,

index-files = true

file-namespaces = ["users.fs.files", "posts.fs.files"]

file-highlighting = true

The above configuration tells monstache that you wish to index the raw content of GridFS files in the users and posts mongodb databases. By default, mongodb uses a bucket named fs, so if you just use the defaults your collection name will be fs.files. However, if you have customized the bucket name, then your file collection would be something like mybucket.files and the entire namespace would be users.mybucket.files.

When you configure monstache this way it will perform an additional operation at startup to ensure the destination indexes in elasticsearch have a field named file with a type mapping of attachment.

For the example TOML configuration above, monstache would initialize 2 indices in preparation for indexing into elasticsearch by issuing the following REST commands:

For elasticsearch versions prior to version 5...

POST /users
{
  "mappings": {
    "fs.files": {
      "properties": {
	"file": { "type": "attachment" }
}}}}

POST /posts
{
  "mappings": {
    "fs.files": {
      "properties": {
	"file": { "type": "attachment" }
}}}}

For elasticsearch version 5 and above...

PUT /_ingest/pipeline/attachment
{
  "description" : "Extract file information",
  "processors" : [
    {
      "attachment" : {
	"field" : "file"
      }
    }
  ]
}

When a file is inserted into mongodb via GridFS, monstache will detect the new file, use the mongodb api to retrieve the raw content, and index a document into elasticsearch with the raw content stored in a file field as a base64 encoded string. The elasticsearch plugin will then extract text content from the raw content using Apache Tika, tokenize the text content, and allow you to query on the content of the file.

To test this feature of monstache you can simply use the mongofiles command to quickly add a file to mongodb via GridFS. Continuing the example above one could issue the following command to put a file named resume.docx into GridFS and after a short time this file should be searchable in elasticsearch in the index users under the type fs.files.

mongofiles -d users put resume.docx

After a short time you should be able to query the contents of resume.docx in the users index in elasticsearch

curl -XGET 'http://localhost:9200/users/fs.files/_search?q=golang'

If you would like to see the text extracted by Apache Tika you can project the appropriate sub-field

For elasticsearch versions prior to version 5...

curl localhost:9200/users/fs.files/_search?pretty -d '{
	"fields": [ "file.content" ],
	"query": {
		"match": {
			"_all": "golang"
		}
	}
}'

For elasticsearch version 5 and above...

curl localhost:9200/users/fs.files/_search?pretty -d '{
	"_source": [ "attachment.content" ],
	"query": {
		"match": {
			"_all": "golang"
		}
	}
}'

When file-highlighting is enabled you can add a highlight clause to your query

For elasticsearch versions prior to version 5...

curl localhost:9200/users/fs.files/_search?pretty -d '{
	"fields": ["file.content"],
	"query": {
		"match": {
			"file.content": "golang"
		}
	},
	"highlight": {
		"fields": {
			"file.content": {
			}
		}
	}
}'

For elasticsearch version 5 and above...

curl localhost:9200/users/fs.files/_search?pretty -d '{
	"_source": ["attachment.content"],
	"query": {
		"match": {
			"attachment.content": "golang"
		}
	},
	"highlight": {
		"fields": {
			"attachment.content": {
			}
		}
	}
}'

The highlight response will contain emphasis on the matching terms

For elasticsearch versions prior to version 5...

"hits" : [ {
	"highlight" : {
		"file.content" : [ "I like to program in <em>golang</em>.\n\n" ]
	}
} ]

For elasticsearch version 5 and above...

"hits" : [{
	"highlight" : {
		"attachment.content" : [ "I like to program in <em>golang</em>." ]
	}
}]