LOG

file source

Thefile source ingests data through one or more local files and outputs log events.

Configuration

  • Common
  • Advanced
vector.toml
[sources.my_source_id]
# REQUIRED - General
type = "file" # example, must be: "file"
include = ["/var/log/nginx/*.log"] # example
# OPTIONAL - General
ignore_older = 86400 # example, no default, seconds
start_at_beginning = true # default
# OPTIONAL - Priority
oldest_first = true # default

Options

14 items
stringoptional

data_dir

The directory used to persist file checkpoint positions. By default, the global[data_dir](#data_dir) option is used. Please make sure the Vector project has write permissions to this dir. See Checkpointing for more info.

No default
View examples
[string]optional

exclude

Array of file patterns to exclude. Globbing is supported. Takes precedence over the include option.

No default
View examples
stringoptional

file_key

The key name added to each event with the full path of the file. See Context for more info.

Default: "file"
View examples
tableoptional

fingerprinting

Configuration for how the file source should identify files.

intbytesoptional

fingerprint_bytes

The number of bytes read off the head of the file to generate a unique fingerprint. See File Identification for more info.

Default: 256
Only relevant when: strategy = "checksum"
View examples
intbytesoptional

ignored_header_bytes

The number of bytes to skip ahead (or ignore) when generating a unique fingerprint. This is helpful if all files share a common header. See File Identification for more info.

No default
Only relevant when: strategy = "checksum"
View examples
stringenumoptional

strategy

The strategy used to uniquely identify files. This is important for checkpointing when file rotation is used.

Default: "checksum"
Enum, must be one of: "checksum" "device_and_inode"
View examples
intmillisecondsoptional

glob_minimum_cooldown

Delay between file discovery calls. This controls the interval at which Vector searches for files. See Auto Discovery and Globbing for more info.

Default: 1000
View examples
stringoptional

host_key

The key name added to each event representing the current host. See Context for more info.

Default: "host"
View examples
commonintsecondsoptional

ignore_older

Ignore files with a data modification date that does not exceed this age.

No default
View examples
common[string]required

include

Array of file patterns to include. Globbing is supported. See File Read Order and File Rotation for more info.

No default
View examples
intbytesoptional

max_line_bytes

The maximum number of a bytes a line can contain before being discarded. This protects against malformed lines or tailing incorrect files.

Default: 102400
View examples
intbytesoptional

max_read_bytes

An approximate limit on the amount of data read from a single file at a given time.

Default: 2048
View examples
stringoptional

message_start_indicator

When present, Vector will aggregate multiple lines into a single event, using this pattern as the indicator that the previous lines should be flushed and a new event started. The pattern will be matched against entire lines as a regular expression, so remember to anchor as appropriate.

No default
View examples
intmillisecondsoptional

multi_line_timeout

Whenmessage_start_indicator is present, this sets the amount of time Vector will buffer lines into a single event before flushing, regardless of whether or not it has seen a line indicating the start of a new message.

Default: 1000
View examples
commonbooloptional

oldest_first

Instead of balancing read capacity fairly across all watched files, prioritize draining the oldest files before moving on to read data from younger files. See File Read Order for more info.

No default
View examples
commonbooloptional

start_at_beginning

When true Vector will read from the beginning of new files, when false Vector will only read new data added to the file. See Read Position for more info.

No default
View examples

Output

This component outputs log events. For example:

{
"file": "/var/log/nginx.log",
"host": "my.host.com",
"message": "Started GET / for 127.0.0.1 at 2012-03-10 14:28:14 +0100",
"timestamp": "2019-11-01T21:15:47+00:00"
}

More detail on the output schema is below.

4 items
stringrequired

file

The full path of the file tha the log originated from. See Checkpointing and Context for more info.

No default
View examples
stringrequired

host

The current hostname, equivalent to the gethostname command.

No default
View examples
stringrequired

message

The raw log message, unaltered.

No default
View examples
timestamprequired

timestamp

The exact time the event was ingested.

No default
View examples

How It Works

Auto Discovery

Vector will continually look for new files matching any of your include patterns. The frequency is controlled via theglob_minimum_cooldown option. If a new file is added that matches any of the supplied patterns, Vector will begin tailing it. Vector maintains a unique list of files and will not tail a file more than once, even if it matches multiple patterns. You can read more about how we identify files in the Identification section.

Checkpointing

Vector checkpoints the current read position in the file after each successful read. This ensures that Vector resumes where it left off if restarted, preventing data from being read twice. The checkpoint positions are stored in the data directory which is specified via the global[data_dir](#data_dir) option but can be overridden via thedata_dir option in thefile sink directly.

Compressed Files

Vector will transparently detect files which have been compressed using gzip and decompress them for reading. This detection process looks for the unique sequence of bytes in the gzip header and does not rely on the compressed files adhering to any kind of naming convention.

One caveat with reading compressed files is that Vector is not able to efficiently seek into them. Rather than implement a potentially-expensive full scan as a seek mechanism, Vector currently will not attempt to make further reads from a file for which it has already stored a checkpoint in a previous run. For this reason, users should take care to allow Vector to fully process any compressed files before shutting the process down or moving the files to another location on disk.

Context

By default, thefile source will add context keys to your events via thefile_key andhost_key options.

Environment Variables

Environment variables are supported through all of Vector's configuration. Simply add ${MY_ENV_VAR} in your Vector configuration file and the variable will be replaced before being evaluated.

You can learn more in the Environment Variables section.

File Deletion

When a watched file is deleted, Vector will maintain its open file handle and continue reading until it reaches EOF. When a file is no longer findable in the includes glob and the reader has reached EOF, that file's reader is discarded.

File Identification

By default, Vector identifies files by creating a cyclic redundancy check (CRC) on the first 256 bytes of the file. This serves as a fingerprint to uniquely identify the file. The amount of bytes read can be controlled via thefingerprint_bytes andignored_header_bytes options.

This strategy avoids the common pitfalls of using device and inode names since inode names can be reused across files. This enables Vector to properly tail files across various rotation strategies.

File Read Order

By default, Vector attempts to allocate its read bandwidth fairly across all of the files it's currently watching. This prevents a single very busy file from starving other independent files from being read. In certain situations, however, this can lead to interleaved reads from files that should be read one after the other.

For example, consider a service that logs to timestamped file, creating a new one at an interval and leaving the old one as-is. Under normal operation, Vector would follow writes as they happen to each file and there would be no interleaving. In an overload situation, however, Vector may pick up and begin tailing newer files before catching up to the latest writes from older files. This would cause writes from a single logical log stream to be interleaved in time and potentially slow down ingestion as a whole, since the fixed total read bandwidth is allocated across an increasing number of files.

To address this type of situation, Vector provides theoldest_first flag. When set, Vector will not read from any file younger than the oldest file that it hasn't yet caught up to. In other words, Vector will continue reading from older files as long as there is more data to read. Only once it hits the end will it then move on to read from younger files.

Whether or not to use theoldest_first flag depends on the organization of the logs you're configuring Vector to tail. If yourinclude glob contains multiple independent logical log streams (e.g. nginx's access.log and error.log, or logs from multiple services), you are likely better off with the default behavior. If you're dealing with a single logical log stream or if you value per-stream ordering over fairness across streams, consider settingoldest_first to true.

File Rotation

Vector supports tailing across a number of file rotation strategies. The default behavior of logrotate is simply to move the old log file and create a new one. This requires no special configuration of Vector, as it will maintain its open file handle to the rotated log until it has finished reading and it will find the newly created file normally.

A popular alternative strategy is copytruncate, in which logrotate will copy the old log file to a new location before truncating the original. Vector will also handle this well out of the box, but there are a couple configuration options that will help reduce the very small chance of missed data in some edge cases. We recommend a combination of delaycompress (if applicable) on the logrotate side and including the first rotated file in Vector'sinclude option. This allows Vector to find the file after rotation, read it uncompressed to identify it, and then ensure it has all of the data, including any written in a gap between Vector's last read and the actual rotation event.

Globbing

Globbing is supported in all provided file paths, files will be autodiscovered continually at a rate defined by theglob_minimum_cooldown option.

Line Delimiters

Each line is read until a new line delimiter (the 0xA byte) or EOF is found.

Read Position

By default, Vector will read new data only for newly discovered files, similar to the tail command. You can read from the beginning of the file by setting thestart_at_beginning option to true.

Previously discovered files will be checkpointed, and the read position will resume from the last checkpoint.