omhiredis: Redis Output Module

Brian Knox <bknox@digitalocean.com>

omhiredis: Redis Output Module
Module Name: omhiredis
Author: Brian Knox <bknox@digitalocean.com>
Contributors: Theo Bertin <theo.bertin@advens.fr>
Purpose
This module provides native support for writing to Redis,
using the hiredis client library.
Configuration Parameters
Note
Parameter names are case-insensitive.
Action Parameters
Server
type default mandatory obsolete legacy directive
word none no none
Name or address of the Redis server
ServerPort
type default mandatory obsolete legacy directive
integer 6379 no none
Port of the Redis server if the server is not listening on the default port.
ServerPassword
type default mandatory obsolete legacy directive
word none no none
Password to support authenticated redis database server to push messages
across networks and datacenters. Parameter is optional if not provided
AUTH command wont be sent to the server.
Mode
type default mandatory obsolete legacy directive
word template no none
Mode to run the output action in: “queue”, “publish”, “set” or “stream” If not supplied, the
original “template” mode is used.
Note
Due to a config parsing bug in 8.13, explicitly setting this to “template” mode will result in a config parsing
error.
If mode is “set”, omhiredis will send SET commands. If “expiration” parameter is provided (see parameter below),
omhiredis will send SETEX commands.
If mode is “stream”, logs will be sent using XADD. In that case, the template-formatted message will be inserted in
the msg field of the stream ID (this behaviour can be controlled through the stream.outField parameter)
 Template
type default mandatory obsolete legacy directive
word RSYSLOG_ForwardFormat no none
Warning
Template is required if using “template” mode.
Key
type default mandatory obsolete legacy directive
word none no none
Key is required if using “publish”, “queue” or “set” modes.
Dynakey
type default mandatory obsolete legacy directive
binary off no none
If set to “on”, the key value will be considered a template by Rsyslog.
Useful when dynamic key generation is desired.
Userpush
type default mandatory obsolete legacy directive
binary off no none
If set to on, use RPUSH instead of LPUSH, if not set or off, use LPUSH.
Expiration
type default mandatory obsolete legacy directive
number 0 no none
Only applicable with mode “set”. Specifies an expiration for the keys set by omhiredis.
If this parameter is not specified, the value will be 0 so keys will last forever, otherwise they will last for X
seconds.
 stream.outField
type default mandatory obsolete legacy directive
word msg no none
Only applicable with mode “stream”.
The stream ID’s field to use to insert the generated log.
Note
Currently, the module cannot use the full message object, so it can only insert templated messages to a single stream entry’s specific field
 stream.capacityLimit
type default mandatory obsolete legacy directive
positive integer 0 no none
Only applicable with mode “stream”.
If set to a value greater than 0 (zero), the XADD will add a MAXLEN option with approximate trimming, limiting the amount of stored entries in the stream at each insertion.
Warning
This parameter has no way to check if the deleted entries have been ACK’ed once or even used, this should be set if you’re sure the insertion rate in lower that the dequeuing to avoid losing entries!
 stream.ack
type default mandatory obsolete legacy directive
boolean off no none
Only applicable with mode “stream”.
If set, the module will send an acknowledgement to Redis, for the stream defined by stream.keyAck, with the group defined by stream.groupAck and the ID defined by stream.indexAck.
This is especially useful when used with the stream.consumerACK deactivated, as it allows omhiredis to acknowledge the correct processing of the log once the job is effectively done.
 stream.del
type default mandatory obsolete legacy directive
boolean off no none
Only applicable with mode “stream”.
If set, the module will send a XDEL command to remove an entry, for the stream defined by stream.keyAck, and the ID defined by stream.indexAck.
This can be useful to automatically remove processed entries extracted on a previous stream by imhiredis.
 stream.keyAck
type default mandatory obsolete legacy directive
word no none
Only applicable with mode “stream”.
Is required, if one of stream.ack or stream.del are on.
Defines the value to use for acknowledging/deleting while inserting a new entry, can be either a constant value or a template name if stream.dynaKeyAck is set.
This can be useful to automatically acknowledge/remove processed entries extracted on a previous stream by imhiredis.
 stream.dynaKeyAck
type default mandatory obsolete legacy directive
boolean off no none
Only applicable with mode “stream”.
If set to on, the value of stream.keyAck is taken as an existing Rsyslog template.
 stream.groupAck
type default mandatory obsolete legacy directive
word no none
Only applicable with mode “stream”.
Is required, if stream.ack is on.
Defines the value to use for acknowledging while inserting a new entry, can be either a constant value or a template name if stream.dynaGroupAck is set.
This can be useful to automatically acknowledge processed entries extracted on a previous stream by imhiredis.
 stream.dynaGroupAck
type default mandatory obsolete legacy directive
boolean off no none
Only applicable with mode “stream”.
If set to on, the value of stream.groupAck is taken as an existing Rsyslog template.
 stream.indexAck
type default mandatory obsolete legacy directive
word no none
Only applicable with mode “stream”.
Is required, if one of stream.ack or stream.del are on.
Defines the index value to use for acknowledging/deleting while inserting a new entry, can be either a constant value or a template name if stream.dynaIndexAck is set.
This can be useful to automatically acknowledge/remove processed entries extracted on a previous stream by imhiredis.
 stream.dynaIndexAck
type default mandatory obsolete legacy directive
boolean off no none
Only applicable with mode “stream”.
If set to on, the value of stream.indexAck is taken as an existing Rsyslog template.
Examples
Example 1: Template mode
In “template” mode, the string constructed by the template is sent
to Redis as a command.
Note
This mode has problems with strings with spaces in them - full message won’t work correctly. In this mode, the template argument is required, and the key argument is meaningless.
module(load="omhiredis")

template(
  name="program_count_tmpl"
  type="string"
  string="HINCRBY progcount %programname% 1")

action(
  name="count_programs"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="template"
  template="program_count_tmpl")
Results
Here’s an example redis-cli session where we HGETALL the counts:
> redis-cli
127.0.0.1:6379> HGETALL progcount
1) "rsyslogd"
2) "35"
3) "rsyslogd-pstats"
4) "4302"
Example 2: Queue mode
In “queue” mode, the syslog message is pushed into a Redis list
at “key”, using the LPUSH command. If a template is not supplied,
the plugin will default to the RSYSLOG_ForwardFormat template.
module(load="omhiredis")

action(
  name="push_redis"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="queue"
  key="my_queue")
Results
Here’s an example redis-cli session where we RPOP from the queue:
> redis-cli
127.0.0.1:6379> RPOP my_queue

"<46>2015-09-17T10:54:50.080252-04:00 myhost rsyslogd: [origin software=\"rsyslogd\" swVersion=\"8.13.0.master\" x-pid=\"6452\" x-info=\"http://www.rsyslog.com\"] start"

127.0.0.1:6379>
Example 3: Publish mode
In “publish” mode, the syslog message is published to a Redis
topic set by “key”.  If a template is not supplied, the plugin
will default to the RSYSLOG_ForwardFormat template.
module(load="omhiredis")

action(
  name="publish_redis"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="publish"
  key="my_channel")
Results
Here’s an example redis-cli session where we SUBSCRIBE to the topic:
> redis-cli

127.0.0.1:6379> subscribe my_channel

Reading messages... (press Ctrl-C to quit)

1) "subscribe"

2) "my_channel"

3) (integer) 1

1) "message"

2) "my_channel"

3) "<46>2015-09-17T10:55:44.486416-04:00 myhost rsyslogd-pstats: {\"name\":\"imuxsock\",\"origin\":\"imuxsock\",\"submitted\":0,\"ratelimit.discarded\":0,\"ratelimit.numratelimiters\":0}"
Example 4: Set mode
In “set” mode, the syslog message is set as a Redis key at “key”. If a template is not supplied,
the plugin will default to the RSYSLOG_ForwardFormat template.
module(load="omhiredis")

action(
  name="set_redis"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="set"
  key="my_key")
Results
Here’s an example redis-cli session where we get the key:
> redis-cli

127.0.0.1:6379> get my_key

"<46>2019-12-17T20:16:54.781239+00:00 localhost rsyslogd-pstats: { \"name\": \"main Q\", \"origin\": \"core.queue\",
\"size\": 3, \"enqueued\": 7, \"full\": 0, \"discarded.full\": 0, \"discarded.nf\": 0, \"maxqsize\": 3 }"

127.0.0.1:6379> ttl my_key

(integer) -1
Example 5: Set mode with expiration
In “set” mode when “expiration” is set to a positive integer, the syslog message is set as a Redis key at “key”,
with expiration “expiration”.
If a template is not supplied, the plugin will default to the RSYSLOG_ForwardFormat template.
module(load="omhiredis")

action(
  name="set_redis"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="set"
  key="my_key"
  expiration="10")
Results
Here’s an example redis-cli session where we get the key and test the expiration:
> redis-cli

127.0.0.1:6379> get my_key

"<46>2019-12-17T20:16:54.781239+00:00 localhost rsyslogd-pstats: { \"name\": \"main Q\", \"origin\": \"core.queue\",
\"size\": 3, \"enqueued\": 7, \"full\": 0, \"discarded.full\": 0, \"discarded.nf\": 0, \"maxqsize\": 3 }"

127.0.0.1:6379> ttl my_key

(integer) 10

127.0.0.1:6379> ttl my_key

(integer) 3

127.0.0.1:6379> ttl my_key

(integer) -2

127.0.0.1:6379> get my_key

(nil)
Example 6: Set mode with dynamic key
In any mode with “key” defined and “dynakey” as “on”, the key used during operation will be dynamically generated
by Rsyslog using templating.
module(load="omhiredis")

template(name="example-template" type="string" string="%hostname%")

action(
  name="set_redis"
  server="my-redis-server.example.com"
  serverport="6379"
  type="omhiredis"
  mode="set"
  key="example-template"
  dynakey="on")
Results
Here’s an example redis-cli session where we get the dynamic key:
> redis-cli

127.0.0.1:6379> keys *

(empty list or set)

127.0.0.1:6379> keys *

1) "localhost"
Example 7: “Simple” stream mode
By using the stream mode, the template-formatted log is inserted in a stream using the stream.outField parameter as key (or msg as default).
The output template can be explicitely set with the Template option (or the default RSYSLOG_ForwardFormat template will be used).
module(load="omhiredis")

template(name="example-template" type="string" string="%hostname%")

action(
  type="omhiredis"
  server="my-redis-server.example.com"
  serverport="6379"
  template="example-template"
  mode="stream"
  key="stream_output"
  stream.outField="data")
Results
Here’s an example redis-cli session where we get the newly inserted stream index:
> redis-cli

127.0.0.1:6379> XLEN stream_output
1

127.0.0.1:6379> xread STREAMS stream_output 0
1) 1) "stream_output"
   2) 1) 1) "1684507855284-0"
         2) 1) "data"
            2) "localhost"
Example 8: Get from a stream with imhiredis, then insert in another one with omhiredis
When you use the omhiredis in stream mode with the imhiredis in stream mode as input, you might want to acknowledge
entries taken with imhiredis once you insert them back somewhere else with omhiredis.
The module allows to acknowledge input entries using information either provided by the user through configuration
or through information accessible in the log entry.
Under the hood, imhiredis adds metadata to the generated logs read from redis streams, this data includes
the stream name, ID of the index, group name and consumer name (when read from a consumer group).
This information is added in the $.redis object and can be retrieved with the help of specific templates.
module(load="imhiredis")
module(load="omhiredis")

template(name="redisJsonMessage" type="list") {
      property(name="$!output")
}

template(name="indexTemplate" type="list") {
      property(name="$.redis!index")
}
# Not used in this example, but can be used to replace the static declarations in omhiredis' configuration below
template(name="groupTemplate" type="list") {
      property(name="$.redis!group")
}
template(name="keyTemplate" type="list") {
      property(name="$.redis!stream")
}

input(type="imhiredis"
        server="127.0.0.1"
        port="6379"
        mode="stream"
        key="stream_input"
        stream.consumerGroup="group1"
        stream.consumerName="consumer1"
        stream.consumerACK="off"
        ruleset="receive_redis")

ruleset(name="receive_redis") {

   action(type="omhiredis"
            server="127.0.0.1"
            serverport="6379"
            mode="stream"
            key="stream_output"
            stream.ack="on"
            # The key and group values are set statically, but the index value is taken from imhiredis metadata
            stream.dynaKeyAck="off"
            stream.keyAck="stream_input"
            stream.dynaGroupAck="off"
            stream.groupAck="group1"
            stream.indexAck="indexTemplate"
            stream.dynaIndexAck="on"
            template="redisJsonMessage"
         )
}
Results
Here’s an example redis-cli session where we get the pending entries at the end of the log re-insertion:
> redis-cli

127.0.0.1:6379> XINFO GROUPS stream_input
1)  1) "name"
   1) "group1"
   2) "consumers"
   3) (integer) 1
   4) "pending"
   5) (integer) 0
   6) "last-delivered-id"
   7) "1684509391900-0"
   8) "entries-read"
   9)  (integer) 1
   10) "lag"
   11) (integer) 0
Example 9: Ensuring streams don’t grow indefinitely
While using Redis streams, index entries are not automatically evicted, even if you acknowledge entries.
You have several options to ensure your streams stays under reasonable memory usage, while making sure your data is
not evicted before being processed.
To do that, you have 2 available options, that can be used independently from each other
(as they don’t apply to the same source):
stream.del to delete processed entries (can also be used as a complement of ACK’ing)
stream.capacityLimit that allows to ensure a hard-limit of logs can be inserted before dropping entries
module(load="imhiredis")
module(load="omhiredis")

template(name="redisJsonMessage" type="list") {
      property(name="$!output")
}

template(name="indexTemplate" type="list") {
      property(name="$.redis!index")
}
template(name="keyTemplate" type="list") {
      property(name="$.redis!stream")
}

input(type="imhiredis"
        server="127.0.0.1"
        port="6379"
        mode="stream"
        key="stream_input"
        ruleset="receive_redis")

ruleset(name="receive_redis") {

   action(type="omhiredis"
            server="127.0.0.1"
            serverport="6379"
            mode="stream"
            key="stream_output"
            stream.capacityLimit="1000000"
            stream.del="on"
            stream.dynaKeyAck="on"
            stream.keyAck="keyTemplate"
            stream.dynaIndexAck="on"
            stream.indexAck="indexTemplate"
            template="redisJsonMessage"
         )
}
Results
Here, the result of this configuration is:
entries are deleted from the source stream stream_input after being inserted by omhiredis to stream_output
stream_output won’t hold more than (approximately) a million entries at a time
Warning
The stream.capacityLimit is an approximate maximum! see redis documentation on MAXLEN and the ‘~’ option to understand how it works!
See also
Help with configuring/using Rsyslog:
Mailing list - best route for general questions
GitHub: rsyslog source project - detailed questions, reporting issues
that are believed to be bugs with Rsyslog
See also
Contributing to Rsyslog:
Source project: rsyslog project README.
Documentation: rsyslog-doc project README
Copyright 2008-2023 Rainer Gerhards (Großrinderfeld),
and Others.

Module Name:	omhiredis
Author:	Brian Knox <bknox@digitalocean.com>
Contributors:	Theo Bertin <theo.bertin@advens.fr>