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mongodb(): Store messages in a MongoDB database

1: Connecting to the MongoDB server

2: mongodb() destination options

The mongodb() driver sends messages to a MongoDB database. MongoDB is a schema-free, document-oriented database. For the list of available optional parameters, see mongodb() destination options.

Declaration

   mongodb(parameters);

The mongodb() driver does not support creating indexes, as that can be a very complex operation in MongoDB. If needed, the administrator of the MongoDB database must ensure that indexes are created on the collections.

The mongodb() driver does not add the _id field to the message: the MongoDB server will do that automatically, if none is present. If you want to override this field from AxoSyslog, use the key() parameter of the value-pairs() option.

The AxoSyslog mongodb() driver is compatible with MongoDB server version 1.4 and newer.

Note

Prior to version 4.0, AxoSyslog handled every data as strings, and allowed you to convert the strings into other types of data that only certain destinations data formats supported.

Starting with AxoSyslog 4.0, each name-value pair is a (name, type, value) triplet, and several components of AxoSyslog have typing support. For details, see Components that support data types.

Example: Using the mongodb() driver

The following example creates a mongodb() destination using only default values.

   destination d_mongodb {
        mongodb();
    };

The following example displays the default values.

   destination d_mongodb {
        mongodb(
            uri("mongodb://localhost:27017/syslog")
            collection("messages")
            value-pairs(
                scope("selected-macros" "nv-pairs" "sdata")
            )
        );
    };

The following example shows the same setup using the deprecated libmongo-client syntax (as used in AxoSyslog version 3.7), and is equivalent with the previous example.

   destination d_mongodb {
        mongodb(
            servers("localhost:27017")
            database("syslog")
            collection("messages")
            value-pairs(
                scope("selected-macros" "nv-pairs" "sdata")
            )
        );
    };

1 - Connecting to the MongoDB server

When AxoSyslog connects the MongoDB server during startup, it completes the following steps.

The AxoSyslog application connects the first address listed in the servers() option.
- If the server is accessible and it is a master MongoDB server, AxoSyslog authenticates on the server (if needed), then starts sending the log messages to the server.
- If the server is not accessible, or it is not a master server in a MongoDB replicaset and it does not send the address of the master server, AxoSyslog connects the next address listed in the servers() option.
- If the server is not a master server in a MongoDB replicaset, but it sends the address of the master server, AxoSyslog connects the received address.
When AxoSyslog connects the master MongoDB server, it retrieves the list of replicas (from the replSet option of the server), and appends this list to the servers() option.
Warning
- This means that AxoSyslog can send log messages to addresses that are not listed in its configuration.
  - Make sure to include the address of your master server in your AxoSyslog configuration file, otherwise you risk losing log messages if all the addresses listed in the AxoSyslog configuration are offline.
  - Addresses retrieved from the MongoDB servers are not stored, and can be lost when AxoSyslog is restarted. The retrieved addresses are not lost if the server() option of the destination was not changed in the configuration file since the last restart.
  - The failover mechanism used in the mongodb() driver is different from the client-side failover used in other drivers.
The AxoSyslog application attempts to connect another server if the servers() list contains at least two addresses, and one of the following events happens:
- The safe-mode() option is set to no, and the MongoDB server becomes unreachable.
- The safe-mode() option is set to yes, and AxoSyslog cannot insert a log message into the database because of an error.
In this case, AxoSyslog starts to connect the addresses in from the servers() list (starting from the first address) to find the new master server, authenticates on the new server (if needed), then continues to send the log messages to the new master server.

During this failover step, one message can be lost if the safe-mode() option is disabled.
If the original master becomes accessible again, AxoSyslog will automatically connect to the original master.

2 - mongodb() destination options

The mongodb() driver sends messages to a MongoDB database. MongoDB is a schema-free, document-oriented database.

The mongodb() destination has the following options:

bulk()


Type:	`yes`, `no`
Default:	`yes`

Available in AxoSyslog version 4.3.0 and newer.

Description: Enables bulk insert mode. If disabled, each messages is inserted individually.

Note: Bulk sending is only efficient if you use a constant collection (without templates), or the used template does not lead to too many collections switching within a reasonable time range.

bulk-bypass-validation()


Type:	`yes`, `no`
Default:	`no`

Available in AxoSyslog version 4.3.0 and newer.

Description: If set to yes, it disables MongoDB bulk operations validation mode.

bulk-unordered()


Type:	`yes`, `no`
Default:	`no`

Available in AxoSyslog version 4.3.0 and newer.

Description: Enables unordered bulk operations mode.

collection()


Type:	template
Default:	messages

Description: The name of the MongoDB collection where the log messages are stored (collections are similar to SQL tables). You can use templates to change the collection dynamically based on the source or the content of the message, for example, collection("${HOST}").

Warning Hazard of data loss! The AxoSyslog application does not verify that the specified collection name does not contain invalid characters. If you specify a collection with an invalid name, the log messages sent to the MongoDB database will be irrevocably lost without any warning.

disk-buffer()

Description: This option enables putting outgoing messages into the disk buffer of the destination to avoid message loss in case of a system failure on the destination side. It has the following options:

capacity-bytes()

Type:	number (bytes)
Default:	1MiB

Description: This is a required option. The maximum size of the disk-buffer in bytes. The minimum value is 1048576 bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old log-disk-fifo-size() option.

In AxoSyslog version 4.2 and earlier, this option was called disk-buf-size().

compaction()

Type:	yes/no
Default:	no

Description: If set to yes, AxoSyslog prunes the unused space in the LogMessage representation, making the disk queue size smaller at the cost of some CPU time. Setting the compaction() argument to yes is recommended when numerous name-value pairs are unset during processing, or when the same names are set multiple times.

Note Simply unsetting these name-value pairs by using the unset() rewrite operation is not enough, as due to performance reasons that help when AxoSyslog is CPU bound, the internal representation of a LogMessage will not release the memory associated with these name-value pairs. In some cases, however, the size of this overhead becomes significant (the raw message size can grow up to four times its original size), which unnecessarily increases the disk queue file size. For these cases, the compaction will drop unset values, making the LogMessage representation smaller at the cost of some CPU time required to perform compaction.

dir()

Type:	string
Default:	N/A

Description: Defines the folder where the disk-buffer files are stored.

Warning

When creating a new dir() option for a disk buffer, or modifying an existing one, make sure you delete the persist file.

AxoSyslog creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the dir() option, then following a restart, AxoSyslog will look for or create disk-buffer files in their old location. To ensure that AxoSyslog uses the new dir() setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to.

Note If the dir() path provided by the user does not exist, AxoSyslog creates the path with the same permission as the running instance.

flow-control-window-bytes()

Type:	number (bytes)
Default:	163840000

Description: Use this option if the option reliable() is set to yes. This option contains the size of the messages in bytes that is used in the memory part of the disk buffer. It replaces the old log-fifo-size() option. It does not inherit the value of the global log-fifo-size() option, even if it is provided. Note that this option will be ignored if the option reliable() is set to no.

In AxoSyslog version 4.2 and earlier, this option was called mem-buf-size().

flow-control-window-size()

Type:	number(messages)
Default:	10000

Description: Use this option if the option reliable() is set to no. This option contains the number of messages stored in overflow queue. It replaces the old log-fifo-size() option. It inherits the value of the global log-fifo-size() option if provided. If it is not provided, the default value is 10000 messages. Note that this option will be ignored if the option reliable() is set to yes.

In AxoSyslog version 4.2 and earlier, this option was called mem-buf-length().

front-cache-size()

Type:	number(messages)
Default:	1000

Description: The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer already exists, the change will take effect when the disk-buffer becomes empty.

Options reliable() and capacity-bytes() are required options.

In AxoSyslog version 4.2 and earlier, this option was called qout-size().

prealloc()

Type:	yes/no
Default:	no

Description:

By default, AxoSyslog doesn’t reserve the disk space for the disk-buffer file, since in a properly configured and sized environment the disk-buffer is practically empty, so a large preallocated disk-buffer file is just a waste of disk space. But a preallocated buffer can prevent other data from using the intended buffer space (and elicit a warning from the OS if disk space is low), preventing message loss if the buffer is actually needed. To avoid this problem, when using AxoSyslog 4.0 or later, you can preallocate the space for your disk-buffer files by setting prealloc(yes).

In addition to making sure that the required disk space is available when needed, preallocated disk-buffer files provide radically better (3-4x) performance as well: in case of an outage the amount of messages stored in the disk-buffer is continuously growing, and using large continuous files is faster, than constantly waiting on a file to change its size.

If you are running AxoSyslog on a dedicated host (always recommended for any high-volume settings), use prealloc(yes).

Available in AxoSyslog 4.0 and later.

reliable()

Type:	yes/no
Default:	no

Description: If set to yes, AxoSyslog cannot lose logs in case of reload/restart, unreachable destination or AxoSyslog crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to no, the normal disk-buffer will be used. This provides a faster, but less reliable disk-buffer option.

Warning Hazard of data loss! If you change the value of reliable() option when there are messages in the disk-buffer, the messages stored in the disk-buffer will be lost.

truncate-size-ratio()

Type:	number((between 0 and 1))
Default:	1 (do not truncate)

Description: Limits the truncation of the disk-buffer file. Truncating the disk-buffer file can slow down the disk IO operations, but it saves disk space. By default, AxoSyslog version 4.0 and later doesn’t truncate disk-buffer files by default (truncate-size-ratio(1)). Earlier versions freed the disk-space when at least 10% of the disk-buffer file could be freed (truncate-size-ratio(0.1)).

AxoSyslog only truncates the file if the possible disk gain is more than truncate-size-ratio() times capacity-bytes().

Smaller values free disk space quicker.
Larger ratios result in better performance.

If you want to avoid performance fluctuations:

use truncate-size-ratio(1) (never truncate), or
use prealloc(yes) to reserve the entire size of the disk-buffer on disk.

Warning Axoflow does not recommend you to change truncate-size-ratio(). Only change its value if you understand the performance implications of doing so.

Example: Examples for using disk-buffer()

In the following case reliable disk-buffer() is used.

destination d_demo {
    network(
        "127.0.0.1"
        port(3333)
        disk-buffer(
            flow-control-window-bytes(10000)
            capacity-bytes(2000000)
            reliable(yes)
            dir("/tmp/disk-buffer")
        )
    );
};

In the following case normal disk-buffer() is used.

destination d_demo {
    network(
        "127.0.0.1"
        port(3333)
            disk-buffer(
            flow-control-window-size(10000)
            capacity-bytes(2000000)
            reliable(no)
            dir("/tmp/disk-buffer")
        )
    );
};

batch-bytes()


Accepted values:	number [bytes]
Default:	none

Description: Sets the maximum size of payload in a batch. If the size of the messages reaches this value, AxoSyslog sends the batch to the destination even if the number of messages is less than the value of the batch-lines() option.

Note that if the batch-timeout() option is enabled and the queue becomes empty, AxoSyslog flushes the messages only if batch-timeout() expires, or the batch reaches the limit set in batch-bytes().

Available in AxoSyslog version 3.19 and later.

batch-lines()


Type:	number
Default:	1

Description: Specifies how many lines are flushed to a destination in one batch. The AxoSyslog application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency.

For example, if you set batch-lines() to 100, AxoSyslog waits for 100 messages.

If the batch-timeout() option is disabled, the AxoSyslog application flushes the messages if it has sent batch-lines() number of messages, or the queue became empty. If you stop or reload AxoSyslog or in case of network sources, the connection with the client is closed, AxoSyslog automatically sends the unsent messages to the destination.

For optimal performance, make sure that the AxoSyslog source that feeds messages to this destination is configured properly: the value of the log-iw-size() option of the source must be higher than the batch-lines()*workers() of the destination. Otherwise, the size of the batches cannot reach the batch-lines() limit.

batch-timeout()


Type:	time in milliseconds
Default:	`-1` (disabled)

Description: Specifies the time AxoSyslog waits for lines to accumulate in the output buffer. The AxoSyslog application sends batches to the destinations evenly. The timer starts when the first message arrives to the buffer, so if only few messages arrive, AxoSyslog sends messages to the destination at most once every batch-timeout() milliseconds.

frac-digits()


Type:	number
Default:	0

Description: The AxoSyslog application can store fractions of a second in the timestamps according to the ISO8601 format. The frac-digits() parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received.

Note The AxoSyslog application can add the fractions to non-ISO8601 timestamps as well.

Note As AxoSyslog is precise up to the microsecond, when the frac-digits() option is set to a value higher than 6, AxoSyslog will truncate the fraction seconds in the timestamps after 6 digits.

hook-commands()

Description: This option makes it possible to execute external programs when the relevant driver is initialized or torn down. The hook-commands() can be used with all source and destination drivers with the exception of the usertty() and internal() drivers.

Note The AxoSyslog application must be able to start and restart the external program, and have the necessary permissions to do so. For example, if your host is running AppArmor or SELinux, you might have to modify your AppArmor or SELinux configuration to enable AxoSyslog to execute external applications.

Using `hook-commands()` when AxoSyslog starts or stops

To execute an external program when AxoSyslog starts or stops, use the following options:

`startup()`

Type:	string
Default:	N/A

Description: Defines the external program that is executed as AxoSyslog starts.

`shutdown()`

Type:	string
Default:	N/A

Description: Defines the external program that is executed as AxoSyslog stops.

Using the hook-commands() when AxoSyslog reloads

To execute an external program when the AxoSyslog configuration is initiated or torn down, for example, on startup/shutdown or during a AxoSyslog reload, use the following options:

`setup()`

Type:	string
Default:	N/A

Description: Defines an external program that is executed when the AxoSyslog configuration is initiated, for example, on startup or during a AxoSyslog reload.

`teardown()`

Type:	string
Default:	N/A

Description: Defines an external program that is executed when the AxoSyslog configuration is stopped or torn down, for example, on shutdown or during a AxoSyslog reload.

Example: Using hook-commands() with a network source

In the following example, the hook-commands() is used with the network() driver and it opens an iptables port automatically as AxoSyslog is started/stopped.

The assumption in this example is that the LOGCHAIN chain is part of a larger ruleset that routes traffic to it. Whenever the AxoSyslog created rule is there, packets can flow, otherwise the port is closed.

source {
    network(transport(udp)
    hook-commands(
          startup("iptables -I LOGCHAIN 1 -p udp --dport 514 -j ACCEPT")
          shutdown("iptables -D LOGCHAIN 1")
        )
     );
};

local-time-zone()


Type:	name of the timezone, or the timezone offset
Default:	The local timezone.

Description: Sets the timezone used when expanding filename and tablename templates.

The timezone can be specified by using the name, for example, time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format, for example, +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

log-fifo-size()


Type:	number
Default:	Use global setting.

Description: The number of messages that the output queue can store.

on-error()

Type:	One of: `drop-message`, `drop-property`, `fallback-to-string`, `silently-drop-message`, `silently-drop-property`, `silently-fallback-to-string`
Default:	Use the global setting (which defaults to `drop-message`)

Description: Controls what happens when type-casting fails and AxoSyslog cannot convert some data to the specified type. By default, AxoSyslog drops the entire message and logs the error. Currently the value-pairs() option uses the settings of on-error().

drop-message: Drop the entire message and log an error message to the internal() source. This is the default behavior of AxoSyslog.
drop-property: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the internal() source.
fallback-to-string: Convert the property to string and log an error message to the internal() source.
silently-drop-message: Drop the entire message silently, without logging the error.
silently-drop-property: Omit the affected property (macro, template, or message-field) silently, without logging the error.
silently-fallback-to-string: Convert the property to string silently, without logging the error.

retries()


Type:	number (of attempts)
Default:	3

Description: If AxoSyslog cannot send a message, it will try again until the number of attempts reaches retries().

If the number of attempts reaches retries(), AxoSyslog will wait for time-reopen() time, then tries sending the message again.

For MongoDB operations, AxoSyslog uses a one-minute timeout: if an operation times out, AxoSyslog assumes the operation has failed.

time-reopen()


Accepted values:	number [seconds]
Default:	60

Description: The time to wait in seconds before a dead connection is reestablished.

throttle()


Type:	number
Default:	0

Description: Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using disk-buffer as well to avoid the risk of losing messages. Specifying 0 or a lower value sets the output limit to unlimited.

uri()


Type:	string
Default:	mongodb://127.0.0.1:27017/syslog?wtimeoutMS=60000&socketTimeoutMS=60000&connectTimeoutMS=60000

Description: Available in AxoSyslog 3.8 and later. Please refer to the MongoDB URI format documentation for detailed syntax.

value-pairs()

Type:	parameter list of the `value-pairs()` option
Default:	`scope("selected-macros" "nv-pairs")`

Description: The value-pairs() option creates structured name-value pairs from the data and metadata of the log message. For details on using value-pairs(), see Structuring macros, metadata, and other value-pairs.

Note Empty keys are not logged.

Note

Prior to version 4.0, AxoSyslog handled every data as strings, and allowed you to convert the strings into other types of data that only certain destinations data formats supported.

Starting with AxoSyslog 4.0, each name-value pair is a (name, type, value) triplet, and several components of AxoSyslog have typing support. For details, see Components that support data types.

workers()


Type:	integer
Default:	1

Description: Specifies the number of worker threads (at least 1) that AxoSyslog uses to send messages to the server. Increasing the number of worker threads can drastically improve the performance of the destination.

Warning Hazard of data loss. When you use more than one worker threads together with disk-based buffering, AxoSyslog creates a separate disk buffer for each worker thread. This means that decreasing the number of workers can result in losing data currently stored in the disk buffer files. Do not decrease the number of workers when the disk buffer files are in use.

write-concern()


Type:	`unacked`, `acked`, or `majority`
Default:	`acked`

Available in AxoSyslog version 4.3.0 and newer.

Description: Sets the write concern mode of the MongoDB operations, for both bulk and single mode.

mongodb(): Store messages in a MongoDB database

Declaration

Example: Using the mongodb() driver

1 - Connecting to the MongoDB server

2 - mongodb() destination options

bulk()

bulk-bypass-validation()

bulk-unordered()

collection()

disk-buffer()

capacity-bytes()

compaction()

dir()

flow-control-window-bytes()

flow-control-window-size()

front-cache-size()

prealloc()

reliable()

truncate-size-ratio()

Example: Examples for using disk-buffer()

batch-bytes()

batch-lines()

batch-timeout()

frac-digits()

hook-commands()

Using hook-commands() when AxoSyslog starts or stops

startup()

shutdown()

Using the hook-commands() when AxoSyslog reloads

setup()

teardown()

Example: Using hook-commands() with a network source

local-time-zone()

log-fifo-size()

on-error()

retries()

time-reopen()

throttle()

uri()

value-pairs()

workers()

write-concern()

Using `hook-commands()` when AxoSyslog starts or stops

`startup()`

`shutdown()`

`setup()`

`teardown()`