Fluentd vs Logstash - Which is better

Fluentd vs. Logstash
Masaki Matsushita
NTT Communications

About Me
● Masaki MATSUSHITA
● Software Engineer at
○ We are providing Internet access here!
● Github: mmasaki Twitter: @_mmasaki
● 16 Commits in Liberty
○ Trove, oslo_log, oslo_config
● CRuby Commiter
○ 100+ commits for performance improvement
2

What are Log Collectors?
● Provide pluggable and unified logging layer
Without Log Collectors With Log Collectors
Images from http://fluentd.org/ 3

Input, Filter and Output
4
Input Plugins
tail
syslog
Filter Plugins
grep
hostname
Output Plugins
InfluxDB
Elasticsearch
● They are implemented as plugins
● Can be replaced easily
Log FIles
Components

Two Popular Log Collectors
● Fluentd
○ Written in CRuby
○ Used in Kubernetes
○ Maintained by Treasure Data Inc.
● Logstash
○ Written in JRuby
○ Maintained by elastic.co
● They have similar features
● Which one is better for you? 5

Agenda
● Comparisons
○ Configuration
○ Supported Plugins
○ Performance
○ Transport Protocol
● Integrate OpenStack with Fluentd/Logstash
○ Considering High Availability 6

Configuration: Fluentd
● Every inputs are tagged
● Logs will be routed by tag
nova-api.log
(tag: openstack.nova)
cinder-api.log
(tag: openstack.cinder)
<match openstack.nova>
<match openstack.cinder>
Filter/Route
7

Fluentd Configuration: Input
<source>
@type tail
path /var/log/nova/nova-api.log
tag openstack.nova
</source>
Example of tailing nova-api log
● Every inputs will be tagged
8

Fluentd Configuration: Output
<match openstack.nova> # nova related logs
@type elasticsearch
host example.com
</match>
<match openstack.*> # all other OpenStack related logs
@type influxdb
# …
</match>
Routed by tag
(First match is priority)
Wildcards can be used
9

Fluentd Configuration: Copy
<match openstack.*>
@type copy
<store>
@type influxdb
</store>
<store>
@type elasticsearch
</store>
</match>
Copy plugin enables multiple
outputs for a tag
Copied Output
tag: openstack.*
10

Logstash Configuration
● No tags
● All inputs will be aggregated
● Logs will be scattered to outputs
nova-api.log
cinder-api.log
Filter/Aggregate
aggregated logs
11

Logstash Configuration
input {
file { path => “/var/log/nova/*.log” }
file { path => “/var/log/cinder/*.log” }
}
output {
elasticsearch { hosts => [“example.com”] }
influxdb { host => “example.com”... }
}
12

Case 1: Separated Streams
Input1
Input2
Input3
Output2
Output3
Output1
● Handle multiple streams separately
13

Case 1: Separated Streams
Fluentd: Simple matching by tag
<match input.input1>
@type output1
</match>
@type output2
</match>
@type output3
</match>
Logstash: Conditional Outputs
output {
if [type] == “input1” {
output1 {}
} else if [type] == “input2” {
output2 {}
} else if [type] == “input3” {
output3 {}
}
}
Need to split aggregated logs
14

Case 2: Aggregated Streams
Input1
Input2
Input3
Output2
Output3
Output1
● Streams will be aggregated and scattered
15

Case 2: Aggregated Streams
Fluentd: Copy plugins is needed
<match input.*>
@type copy
<store>
@type output1
</store>
<store>
@type output2
</store>
<store>
@type output3
</store>
</match>
Logstash: Quite simple
output {
output1 {}
output2 {}
output3 {}
}
16

Configuration
● Fluentd
○ Routed by simple tag matching
○ Suited to handle log streams separately
● Logstash
○ Logs are aggregated
○ Suited to handle logs in gather-scatter style
17

Plugins
● Both provide many plugins
○ Fluentd: 300+, Logstash: 200+
● Popular plugins are bundled with Logstash
○ They are maintained by the Logstash project
● Fluentd contains only minimal plugins
○ Most plugins are maintained by individuals
● Plugins can be installed easily by one command
18

Performance
● Depends on circumstances
● More than enough for OpenStack logs
○ Both can handle 10000+ logs/s
● Applying heavy filters is not a good idea
● CRuby is slow because of GVL?
○ GVL: Global VM (Interpreter) Lock
○ It’s not true for IO bound loads
19

GVL on IO bound loads
● IO operation can be performed in parallel
20
Thread 1 Thread 2
Idle :
User Space:
Kernel Space:
Actual Read/Write
Ruby Code Execution
GVL Released/
Acquired
IO operations
in parallel

Transport Protocol
● Both collectors have their own transport protocol.
○ Failure Detection and Fallback
● Logstash: Lumberjack protocol
○ Active-Standby only
● Fluentd: forward protocol
○ Active-Active (Load Balancing), Active-Standby
○ Some additional features
21

Logstash Transport: lumberjack
● Active-Standby lumberjack { #config@source
hosts => [
“primary”,
“secondary”
]
port => 1234
ssl_certificate => …
}
primary
secondary
source
secondary is used
when primary fails
Fail
Fallback
22

Fluentd Transport: forward
● Active-Active
(Load Balancing)
<match openstack.*>
type forward
<server>
host dest1
</server>
<server>
host dest2
</server>
</match>
source dest1
dest2
Equally balanced
outputs
23

● Active-Standby <match openstack.*>
type forward
<server>
host primary
</server>
<server>
host secondary
standby
</server>
</match>
primary
secondary
source
Fail
Fallback
24

● Weighted Load Balancing
<match openstack.*>
type forward
<server>
host dest1
weight 60
</server>
<server>
host dest2
weight 40
</server>
</match>
source dest1
dest2
60%
40%
25

● At-least-one Semantics
(may affect performance)
<match openstack.*>
type forward
require_ack_response
<server>
host dest
</server>
</match>
destsource
send logs
ACK
Logs are re-transmitted
until ACK is received
26

Transport Protocol
● Both can be configured as Active-Standby mode.
● Fluentd has great features:
○ Active-Active Mode (Load Balancing)
○ At-least-one Semantics
○ Weighted Load Balancing
27

Forwarders
● Fluentd/Logstash have their own “forwarders”
○ Lightweight implementation written in Golang
○ Low memory consumption
○ One binary: Less dependent and easy to install
28
Node
Tail log files
Forwarder
Log AggregatorForward/
Lumberjack
Protocol

Forwarders: Config Example
fluentd-forwarder:
[fluentd-forwarder]
to = fluent://fluentd1:24224
to = fluent://fluentd2:24224
logstash-forwarder:
"network": {
"servers": [
"logstash1:5043",
"logstash2:5043"
]
}Always send logs to both servers.
Pick one active server and send logs only to it.
Fallback to another server on failure. 29

Integration with OpenStack
● Tail log files by local Fluentd/Logstash
○ must parse many form of log files
● Rsyslog
○ installed by default in most distribution
○ can receive logs in JSON format
● Direct output from oslo_log
○ oslo_log: logging library used by components
○ Logging without any parsing 30

Log
Aggregators
OpenStack nodes
Tail Log Files
31
Tail log files
Forward Protocol
dest1
dest2

Tail Log Files
• Must handle many log files…
syslog
kern.log
apache2/access.log
apache2/error.log
keystone/keystone-all.log
keystone/keystone-manage.log
keystone/keystone.log
cinder/cinder-api.log
cinder/cinder-scheduler.log
neutron/neutron-server.log
neutron/neutron-server.log
nova/nova-api.log
nova/nova-conductor.log
nova/nova-consoleauth.log
nova/nova-manage.log
nova/nova-novncproxy.log
nova/nova-scheduler.log
mysql/error.log
mysql/mysql-slow.log
mysql.log
mysql.err
nova/nova-compute.log
nova/nova-manage.log...
32

Tail Log Files
• But you can use wildcard
Fluentd:
<source>
type tail
path /var/log/nova/*.log
tag openstack.nova
</source>
Logstash:
input {
file {
path => [“/var/log/nova/*.log”]
}
}
33

Parse Text Log
● Welcome to regular expression hell!
<source>
type tail # or syslog
path /var/log/nova/nova-api.log
format /^(?<asctime>.+) (?<process>d+) (?<loglevel>w+) (?
<objname>S+)( [(-|(?<request_id>.+?) (?<user_identity>.+))])?
((?<remote>S*) "(?<method>S+) (?<path>[^"]*) S*?" status: (?
<code>d*) len: (?<size>d*) time: (?<res_time>S)|(?<message>.
*))/
</source>
34

Log
Aggregators
OpenStack nodes
Rsyslog
35
via /dev/log
Syslog Protocol
(TCP or UDP)
rsyslog

Rsyslog: Logging.conf
● Logging Configuration in detail
● Handler: Syslog, Formatter: JSON
# /etc/{nova,cinder…}/logging.conf
[handler_syslog]
class = handlers.SysLogHandler
args = ('/dev/log', handlers.SysLogHandler.LOG_LOCAL1)
formatter = json
[formatter_json]
class = oslo_log.formatters.JSONFormatter 36

Example Output: JSONFormatter
{
"levelname": "INFO",
"funcname": "start",
"message": "Starting conductor node (version 13.0.0)",
"msg": "Starting %(topic)s node (version %(version)s)",
"asctime": "2015-09-29 18:29:57,690",
"relative_created": 2454.8499584198,
"process": 25204,
"created": 1443518997.690932,
"thread": 140119466896752,
"name": "nova.service",
"process_name": "MainProcess",
"thread_name": "GreenThread-1",
...
37

Syslog Facilities
● Assignment of local0..7 Facilities for components
● Logs are tagged as like “syslog.local0” in Fluentd
● Example:
○ local0: Keystone
○ local1: Nova
○ local2: Cinder
○ local3: Neutron
○ local4: Glance
38

Rsyslog: Config@OpenStack nodes
● Active-Standby Configuration
# /etc/rsyslog.d/rsyslog.conf
user.* @@primary:5140
$ActionExecOnlyWhenPreviousIsSuspended on
&@@secondary:5140
39

Rsyslog: Config@Aggregator
Fluentd:
<source>
type syslog
port 5140
protocol_type tcp
format json
tag syslog
</source>
Logstash:
input {
syslog {
codec => json
port => 5140
}
} Listen on both TCP and UDP
Specify TCP or UDP 40

Rsyslog: Config@Aggregator
Fluentd:
<source>
type syslog
port 5140
protocol_type tcp
format json
tag syslog
</source>
Logstash:
input {
syslog {
codec => json
port => 5140
}
}
41

Log
AggregatorsOpenStack nodes
42
via FluentHandler
Forward Protocol
Direct output from oslo_log
Local Fluentd for buffering/load balancing
(Logstash also can be used)

Direct output from oslo_log
# logging.conf:
[handler_fluent]
class = fluent.handler.FluentHandler # fluent-logger
formatter = fluent
args = (’openstack.nova', 'localhost', 24224)
[formatter_fluent]
class = fluent.handler.FluentFormatter # our Blueprint
43
Format logs as Dictionary

Our BP in oslo_log: FluentFormatter
{
"hostname":"allinone-vivid",
"extra":{"project":"unknown","version":"unknown"},
"process_name":"MainProcess",
"module":"wsgi",
"message":"(4132) wsgi starting up on http://0.0.0.0:8774/",
"filename":"wsgi.py",
"name":"nova.osapi_compute.wsgi.server",
"level":"INFO",
"traceback":null,
"funcname":"server",
"time":"2015-10-15 10:09:12,255"
}
Don’t need to parse!
44

Conclusion
● Log Handling
○ Fluentd: Logs are distinguished by tag
○ Logstash: No tags. Logs are aggregated
● Transport Protocol
○ Both supports active-standby mode
○ Fluentd supports some additional features
■ Client-side load balancing (Active-Active)
■ At-least-one semantics
■ Weighted load balancing 45

Conclusion
● Integration with OpenStack
○ Tail log files: regular expression hell
○ Rsyslog: No agents are needed
○ Direct output from oslo_log w/o any parsing
○ Review is welcome for our Blueprint
(oslo_log: fluent-formatter)
46

Thank you!
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Fluentd vs Logstash - Which is better

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