Overview

This is a simple mongodb backend for Lager. It sends messages from lager to the configured mongodb server. In order to minimises delays due to logging DB writes are ‘unsafe_ok’ (no wait for confirmation that the write succeded).

Configuration

You can override the the following (defaults in brackets)

• mongo server (“127.0.0.1”)

• database (the atom ‘log’)
• log_level (the atom ‘debug’) - see lager documentation for allowable options
  • node (default ‘true’) - if true each log has an entry of node() added, if false

  no entry is written, if any other value, it is passed through unchanged (somewhat like tag)

  • tag (default ‘undefined’ - no tag entry written by default) - if present the tag

  is added to all entries (for example to distinguish between entries from multiple clients).

The configuration is read at start-up from the lager backend configuration, an example of which is shown below:

{lager_mongo, [{log_database, test_log_database}, 
               {tag, "my tag"},
	       {node, false},
	       {log_level, info},
	       {collection, test_collection}]}, 

You can also change config once the backend is loaded (for example to change tag data once the system is up and running). This is done by calling lager_mongo:update_params([…list of param data]). Note that this does not presently cause a new connection to the mongo server to be created, so changes to mongo server data are ignored - database and collection changes are processed.

Below is sample mongo output (from running the test within the module). The back end tries to break out file/function/line number for entries with parse_transform information in them. This is likely to be fragile! If it can’t parse what it get it slaps whatever data it has into the “pid” field (as in the first two entries).

> db.test_collection.find().toArray()
[
	{
		"_id" : ObjectId("4f2074a34fcf89192b000001"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 7,
		"tag" : "my tag",
		"pid" : "<0.43.0>",
		"message" : "Lager installed handler lager_mongo into lager_event"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000002"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 7,
		"tag" : "my tag",
		"pid" : "<0.52.0>",
		"message" : "Lager installed handler {lager_file_backend,\"error.log\"} into lager_event"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000003"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 7,
		"tag" : "my tag",
		"pid" : "<0.53.0>",
		"message" : "Lager installed handler {lager_file_backend,\"console.log\"} into lager_event"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000004"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 6,
		"tag" : "my tag",
		"pid" : "<0.32.0>",
		"message" : "Test INFO message"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000005"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 7,
		"tag" : "my tag",
		"pid" : "<0.32.0>",
		"message" : "Test DEBUG message"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000006"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 3,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"node" : "nonode@nohost",
		"message" : "Test ERROR message"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000007"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 4,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"module" : "lager_mongo",
		"function" : "test_",
		"line" : 264,
		"node" : "nonode@nohost",
		"message" : "Hello"
	},
	{
		"_id" : ObjectId("4f2074a34fcf89192b000008"),
		"datetime" : ISODate("2012-01-25T21:31:15Z"),
		"level" : 6,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"module" : "lager_mongo",
		"function" : "test_",
		"line" : 265,
		"node" : "nonode@nohost",
		"message" : "Info \"variable\""
	},
	{
		"_id" : ObjectId("4f2075334fcf89192b000009"),
		"datetime" : ISODate("2012-01-25T21:33:39Z"),
		"level" : 6,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"node" : "nonode@nohost",
		"message" : "Test INFO message"
	},
	{
		"_id" : ObjectId("4f2075334fcf89192b00000a"),
		"datetime" : ISODate("2012-01-25T21:33:39Z"),
		"level" : 7,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"node" : "nonode@nohost",
		"message" : "Test DEBUG message"
	},
	{
		"_id" : ObjectId("4f2075334fcf89192b00000b"),
		"datetime" : ISODate("2012-01-25T21:33:39Z"),
		"level" : 3,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"node" : "nonode@nohost",
		"message" : "Test ERROR message"
	},
	{
		"_id" : ObjectId("4f2075334fcf89192b00000c"),
		"datetime" : ISODate("2012-01-25T21:33:39Z"),
		"level" : 4,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"module" : "lager_mongo",
		"function" : "test_",
		"line" : 259,
		"node" : "nonode@nohost",
		"message" : "Hello"
	},
	{
		"_id" : ObjectId("4f2075334fcf89192b00000d"),
		"datetime" : ISODate("2012-01-25T21:33:39Z"),
		"level" : 6,
		"tag" : "Updated tag",
		"pid" : "<0.32.0>",
		"module" : "lager_mongo",
		"function" : "test_",
		"line" : 260,
		"node" : "nonode@nohost",
		"message" : "Info \"variable\""
	}
]

Refer to Lager’s documentation for futher information on configuring handlers.