log
Enables and configures HTTP request logging (also known as access logs).
The log
directive applies to the host/port of the site block it appears in, not any other part of the site address (e.g. path).
Syntax
log { output <writer_module> ... format <encoder_module> ... level <level> }
- output configures where to write the logs. See Output modules below. Default:
stderr
- format describes how to encode, or format, the logs. See Format modules below. Default:
console
ifstdout
is detected to be a terminal,json
otherwise. - level is the minimum entry level to log. Default:
INFO
. Note that access logs currently only emitINFO
andERROR
level logs.
Output modules
The output subdirective lets you customize where logs get written. It appears within a log
block.
stderr
Standard error (console, default).
output stderr
stdout
Standard output (console).
output stdout
discard
No output.
output discard
file
A file. By default, log files are rotated ("rolled") to prevent disk space exhaustion.
output file <filename> { roll_disabled roll_size <size> roll_keep <num> roll_keep_for <days> }
- <filename> is the path to the log file.
- roll_disabled disables log rolling. This can lead to disk space depletion, so only use this if your log files are maintained some other way.
- roll_size is the size at which to roll the log file. The current implementation supports megabyte resolution; fractional values are rounded up to the next whole megabyte. For example,
1.1MiB
is rounded up to2MiB
. Default:100MiB
- roll_keep is how many log files to keep before deleting the oldest ones. Default:
10
- roll_keep_for is how long to keep rolled files as a duration string. The current implementation supports day resolution; fractional values are rounded up to the next whole day. For example,
36h
(1.5 days) is rounded up to48h
(2 days). Default:2160h
(90 days)
net
A network socket. If the socket goes down, it will dump logs to stderr while it attempts to reconnect.
output net <address> { dial_timeout <duration> }
- <address> is the address to write logs to.
- dial_timeout is how long to wait for a successful connection to the log socket. Log emissions may be blocked for up to this long if the socket goes down.
Format modules
The format subdirective lets you customize how logs get encoded (formatted). It appears within a log
block.
In addition to the syntax for each individual encoder, these common properties can be set on most encoders:
format <encoder_module> { message_key <key> level_key <key> time_key <key> name_key <key> caller_key <key> stacktrace_key <key> line_ending <char> time_format <format> level_format <format> }
- message_key The key for the message field of the log entry. Default:
msg
- level_key The key for the level field of the log entry. Default:
level
- time_key The key for the time field of the log entry. Default:
ts
- name_key The key for the name field of the log entry (i.e. the name of the logger itself). Default:
name
- caller_key The key for the caller field of the log entry.
- stacktrace_key The key for the stacktrace field of the log entry.
- line_ending The line endings to use.
- time_format The format for timestamps.
- level_format The format for levels.
console
The console encoder formats the log entry for human readability while preserving some structure.
format console
json
Formats each log entry as a JSON object.
format json
single_field
⚠️ This format is deprecated, and will be removed in a future version.
Writes only a single field from the structure log entry. Useful if one of the fields has all the information you need.
format single_field <field_name>
- <field_name> is the name of the field whose value to use as the log entry.
filter
Wraps another encoder module, allowing per-field filtering.
format filter { wrap <encode_module> ... fields { <field> <filter> ... } }
Nested fields can be referenced by representing a layer of nesting with >
. In other words, for an object like {"a":{"b":0}}
, the inner field can be referenced as a>b
.
The following fields are fundamental to the log and cannot be filtered because they are added by the underlying logging library as special cases: ts
, level
, logger
, and msg
.
These are the available filters:
delete
Marks a field to be skipped from being encoded.
<field> delete
replace
Marks a field to be replaced with the provided string at encoding time.
<field> replace <replacement>
ip_mask
Masks IP addresses in the field using a CIDR mask, i.e. the number of bytes from the IP to retain, starting from the left side. There is separate configuration for IPv4 and IPv6 addresses.
<field> ip_mask { ipv4 <cidr> ipv6 <cidr> }
Examples
Enable access logging (to the console):
log
Write logs to a file (with log rolling, which is enabled by default):
log { output file /var/log/access.log }
Customize log rolling:
log { output file /var/log/access.log { roll_size 1gb roll_keep 5 roll_keep_for 720h } }
Use Common Log Format (CLF):
⚠️ The single_field
format is deprecated and will be removed in a future version. To encode logs in common log format, please use the format-encoder
plugin.
log { format single_field common_log }
Delete the Authorization request header from the logs:
log { format filter { wrap console fields { request>headers>Authorization delete } } }
Mask the remote address from the request, keeping the first 16 bytes (i.e. 255.255.0.0) for IPv4 addresses, and the first 64 bytes from IPv6 addresses, and also deletes the common_log
field which would normally contain an unmasked IP address:
log { format filter { wrap console fields { common_log delete request>remote_addr ip_mask { ipv4 24 ipv6 32 } } } }