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filestream input

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filestream input

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Use the filestream input to read lines from active log files. It is the new, improved alternative to the log input. It comes with various improvements to the existing input:

Checking of close_* options happens out of band. Thus, if an output is blocked, Filebeat can close the reader and avoid keeping too many files open.
Detailed metrics are available for all files that match the paths configuration regardless of the harvester_limit. This way, you can keep track of all files, even ones that are not actively read.
The order of parsers is configurable. So it is possible to parse JSON lines and then aggregate the contents into a multiline event.
Some position updates and metadata changes no longer depend on the publishing pipeline. If the pipeline is blocked some changes are still applied to the registry.
Only the most recent updates are serialized to the registry. In contrast, the log input has to serialize the complete registry on each ACK from the outputs. This makes the registry updates much quicker with this input.
The input ensures that only offsets updates are written to the registry append only log. The log writes the complete file state.
Stale entries can be removed from the registry, even if there is no active input.

To configure this input, specify a list of glob-based paths that must be crawled to locate and fetch the log lines.

Example configuration:

filebeat.inputs:
- type: filestream
  paths:
    - /var/log/messages
    - /var/log/*.log

You can apply additional configuration settings (such as fields, include_lines, exclude_lines and so on) to the lines harvested from these files. The options that you specify are applied to all the files harvested by this input.

To apply different configuration settings to different files, you need to define multiple input sections:

filebeat.inputs:
- type: filestream 
  paths:
    - /var/log/system.log
    - /var/log/wifi.log
- type: filestream 
  paths:
    - "/var/log/apache2/*"
  fields:
    apache: true

	Harvests lines from two files: `system.log` and `wifi.log`.
	Harvests lines from every file in the `apache2` directory, and uses the `fields` configuration option to add a field called `apache` to the output.

Reading files on network shares and cloud providers

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However, one of the limitations of these data sources can be mitigated if you configure Filebeat adequately.

By default, Filebeat identifies files based on their inodes and device IDs. However, on network shares and cloud providers these values might change during the lifetime of the file. If this happens Filebeat thinks that file is new and resends the whole content of the file. To solve this problem you can configure file_identity option. Possible values besides the default inode_deviceid are path and inode_marker.

Changing file_identity methods between runs may result in duplicated events in the output.

Selecting path instructs Filebeat to identify files based on their paths. This is a quick way to avoid rereading files if inode and device ids might change. However, keep in mind if the files are rotated (renamed), they will be reread and resubmitted.

The option inode_marker can be used if the inodes stay the same even if the device id is changed. You should choose this method if your files are rotated instead of path if possible. You have to configure a marker file readable by Filebeat and set the path in the option path of inode_marker.

The content of this file must be unique to the device. You can put the UUID of the device or mountpoint where the input is stored. The following example oneliner generates a hidden marker file for the selected mountpoint /logs: Please note that you should not use this option on Windows as file identifiers might be more volatile.

$ lsblk -o MOUNTPOINT,UUID | grep /logs | awk '{print $2}' >> /logs/.filebeat-marker

To set the generated file as a marker for file_identity you should configure the input the following way:

filebeat.inputs:
- type: filestream
  paths:
    - /logs/*.log
  file_identity.inode_marker.path: /logs/.filebeat-marker

Reading from rotating logs

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When dealing with file rotation, avoid harvesting symlinks. Instead use the paths setting to point to the original file, and specify a pattern that matches the file you want to harvest and all of its rotated files. Also make sure your log rotation strategy prevents lost or duplicate messages. For more information, see Log rotation results in lost or duplicate events.

Furthermore, to avoid duplicate of rotated log messages, do not use the path method for file_identity. Or exclude the rotated files with exclude_files option.

Prospector options

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The prospector is running a file system watcher which looks for files specified in the paths option. At the moment only simple file system scanning is supported.

`paths`

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A list of glob-based paths that will be crawled and fetched. All patterns supported by Go Glob are also supported here. For example, to fetch all files from a predefined level of subdirectories, the following pattern can be used: /var/log/*/*.log. This fetches all .log files from the subfolders of /var/log. It does not fetch log files from the /var/log folder itself. It is possible to recursively fetch all files in all subdirectories of a directory using the optional recursive_glob settings.

Filebeat starts a harvester for each file that it finds under the specified paths. You can specify one path per line. Each line begins with a dash (-).

Scanner options

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The scanner watches the configured paths. It scans the file system periodically and returns the file system events to the Prospector.

`prospector.scanner.recursive_glob`

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Enable expanding ** into recursive glob patterns. With this feature enabled, the rightmost ** in each path is expanded into a fixed number of glob patterns. For example: /foo/** expands to /foo, /foo/*, /foo/*/*, and so on. If enabled it expands a single ** into a 8-level deep * pattern.

This feature is enabled by default. Set prospector.scanner.recursive_glob to false to disable it.

`prospector.scanner.exclude_files`

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A list of regular expressions to match the files that you want Filebeat to ignore. By default no files are excluded.

The following example configures Filebeat to ignore all the files that have a gz extension:

filebeat.inputs:
- type: filestream
  ...
  prospector.scanner.exclude_files: ['\.gz$']

See Regular expression support for a list of supported regexp patterns.

`prospector.scanner.include_files`

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A list of regular expressions to match the files that you want Filebeat to include. If a list of regexes is provided, only the files that are allowed by the patterns are harvested.

By default no files are excluded. This option is the counterpart of prospector.scanner.exclude_files.

The following example configures Filebeat to exclude files that are not under /var/log:

filebeat.inputs:
- type: filestream
  ...
  prospector.scanner.include_files: ['^/var/log/.*']

Patterns should start with ^ in case of absolute paths.

See Regular expression support for a list of supported regexp patterns.

`prospector.scanner.symlinks`

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The symlinks option allows Filebeat to harvest symlinks in addition to regular files. When harvesting symlinks, Filebeat opens and reads the original file even though it reports the path of the symlink.

When you configure a symlink for harvesting, make sure the original path is excluded. If a single input is configured to harvest both the symlink and the original file, Filebeat will detect the problem and only process the first file it finds. However, if two different inputs are configured (one to read the symlink and the other the original path), both paths will be harvested, causing Filebeat to send duplicate data and the inputs to overwrite each other’s state.

The symlinks option can be useful if symlinks to the log files have additional metadata in the file name, and you want to process the metadata in Logstash. This is, for example, the case for Kubernetes log files.

Because this option may lead to data loss, it is disabled by default.

`prospector.scanner.resend_on_touch`

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If this option is enabled a file is resent if its size has not changed but its modification time has changed to a later time than before. It is disabled by default to avoid accidentally resending files.

`prospector.scanner.check_interval`

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How often Filebeat checks for new files in the paths that are specified for harvesting. For example, if you specify a glob like /var/log/*, the directory is scanned for files using the frequency specified by check_interval. Specify 1s to scan the directory as frequently as possible without causing Filebeat to scan too frequently. We do not recommend to set this value <1s.

If you require log lines to be sent in near real time do not use a very low check_interval but adjust close.on_state_change.inactive so the file handler stays open and constantly polls your files.

The default setting is 10s.

`ignore_older`

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If this option is enabled, Filebeat ignores any files that were modified before the specified timespan. Configuring ignore_older can be especially useful if you keep log files for a long time. For example, if you want to start Filebeat, but only want to send the newest files and files from last week, you can configure this option.

You can use time strings like 2h (2 hours) and 5m (5 minutes). The default is 0, which disables the setting. Commenting out the config has the same effect as setting it to 0.

You must set ignore_older to be greater than close.on_state_change.inactive.

The files affected by this setting fall into two categories:

Files that were never harvested
Files that were harvested but weren’t updated for longer than ignore_older

For files which were never seen before, the offset state is set to the end of the file. If a state already exists, the offset is not changed. If a file is updated again later, reading continues at the set offset position.

The ignore_older setting relies on the modification time of the file to determine if a file is ignored. If the modification time of the file is not updated when lines are written to a file (which can happen on Windows), the ignore_older setting may cause Filebeat to ignore files even though content was added at a later time.

To remove the state of previously harvested files from the registry file, use the clean_inactive configuration option.

Before a file can be ignored by Filebeat, the file must be closed. To ensure a file is no longer being harvested when it is ignored, you must set ignore_older to a longer duration than close.on_state_change.inactive.

If a file that’s currently being harvested falls under ignore_older, the harvester will first finish reading the file and close it after close.on_state_change.inactive is reached. Then, after that, the file will be ignored.

`ignore_inactive`

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If this option is enabled, Filebeat ignores every file that has not been updated since the selected time. Possible options are since_first_start and since_last_start. The first option ignores every file that has not been updated since the first start of Filebeat. It is useful when the Beat might be restarted due to configuration changes or a failure. The second option tells the Beat to read from files that have been updated since its start.

The files affected by this setting fall into two categories:

Files that were never harvested
Files that were harvested but weren’t updated since ignore_inactive.

For files that were never seen before, the offset state is set to the end of the file. If a state already exist, the offset is not changed. In case a file is updated again later, reading continues at the set offset position.

The setting relies on the modification time of the file to determine if a file is ignored. If the modification time of the file is not updated when lines are written to a file (which can happen on Windows), the setting may cause Filebeat to ignore files even though content was added at a later time.

To remove the state of previously harvested files from the registry file, use the clean_inactive configuration option.

`close.*`

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The close.* configuration options are used to close the harvester after a certain criteria or time. Closing the harvester means closing the file handler. If a file is updated after the harvester is closed, the file will be picked up again after prospector.scanner.check_interval has elapsed. However, if the file is moved or deleted while the harvester is closed, Filebeat will not be able to pick up the file again, and any data that the harvester hasn’t read will be lost.

The close.on_state_change.* settings are applied asynchronously to read from a file, meaning that if Filebeat is in a blocked state due to blocked output, full queue or other issue, a file that would be closed regardless.

`close.on_state_change.inactive`

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When this option is enabled, Filebeat closes the file handle if a file has not been harvested for the specified duration. The counter for the defined period starts when the last log line was read by the harvester. It is not based on the modification time of the file. If the closed file changes again, a new harvester is started and the latest changes will be picked up after prospector.scanner.check_interval has elapsed.

We recommended that you set close.on_state_change.inactive to a value that is larger than the least frequent updates to your log files. For example, if your log files get updated every few seconds, you can safely set close.on_state_change.inactive to 1m. If there are log files with very different update rates, you can use multiple configurations with different values.

Setting close.on_state_change.inactive to a lower value means that file handles are closed sooner. However this has the side effect that new log lines are not sent in near real time if the harvester is closed.

The timestamp for closing a file does not depend on the modification time of the file. Instead, Filebeat uses an internal timestamp that reflects when the file was last harvested. For example, if close.on_state_change.inactive is set to 5 minutes, the countdown for the 5 minutes starts after the harvester reads the last line of the file.

You can use time strings like 2h (2 hours) and 5m (5 minutes). The default is 5m.

`close.on_state_change.renamed`

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Only use this option if you understand that data loss is a potential side effect.

When this option is enabled, Filebeat closes the file handler when a file is renamed. This happens, for example, when rotating files. By default, the harvester stays open and keeps reading the file because the file handler does not depend on the file name. If the close.on_state_change.renamed option is enabled and the file is renamed or moved in such a way that it’s no longer matched by the file patterns specified for the , the file will not be picked up again. Filebeat will not finish reading the file.

Do not use this option when path based file_identity is configured. It does not make sense to enable the option, as Filebeat cannot detect renames using path names as unique identifiers.

WINDOWS: If your Windows log rotation system shows errors because it can’t rotate the files, you should enable this option.

`close.on_state_change.removed`

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When this option is enabled, Filebeat closes the harvester when a file is removed. Normally a file should only be removed after it’s inactive for the duration specified by close.on_state_change.inactive. However, if a file is removed early and you don’t enable close.on_state_change.removed, Filebeat keeps the file open to make sure the harvester has completed. If this setting results in files that are not completely read because they are removed from disk too early, disable this option.

This option is enabled by default. If you disable this option, you must also disable clean.on_state_change.removed.

WINDOWS: If your Windows log rotation system shows errors because it can’t rotate files, make sure this option is enabled.

`close.reader.eof`

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Only use this option if you understand that data loss is a potential side effect.

When this option is enabled, Filebeat closes a file as soon as the end of a file is reached. This is useful when your files are only written once and not updated from time to time. For example, this happens when you are writing every single log event to a new file. This option is disabled by default.

`close.reader.after_interval`

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Only use this option if you understand that data loss is a potential side effect. Another side effect is that multiline events might not be completely sent before the timeout expires.

When this option is enabled, Filebeat gives every harvester a predefined lifetime. Regardless of where the reader is in the file, reading will stop after the close.reader.after_interval period has elapsed. This option can be useful for older log files when you want to spend only a predefined amount of time on the files. While close.reader.after_interval will close the file after the predefined timeout, if the file is still being updated, Filebeat will start a new harvester again per the defined scan_frequency. And the close.reader.after_interval for this harvester will start again with the countdown for the timeout.

This option is particularly useful in case the output is blocked, which makes Filebeat keep open file handlers even for files that were deleted from the disk. Setting close.reader.after_interval to 5m ensures that the files are periodically closed so they can be freed up by the operating system.

If you set close.reader.after_interval to equal ignore_older, the file will not be picked up if it’s modified while the harvester is closed. This combination of settings normally leads to data loss, and the complete file is not sent.

When you use close.reader.after_interval for logs that contain multiline events, the harvester might stop in the middle of a multiline event, which means that only parts of the event will be sent. If the harvester is started again and the file still exists, only the second part of the event will be sent.

This option is set to 0 by default which means it is disabled.

`clean_*`

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The clean_* options are used to clean up the state entries in the registry file. These settings help to reduce the size of the registry file and can prevent a potential inode reuse issue.

`clean_inactive`

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Only use this option if you understand that data loss is a potential side effect.

When this option is enabled, Filebeat removes the state of a file after the specified period of inactivity has elapsed. The state can only be removed if the file is already ignored by Filebeat (the file is older than ignore_older). The clean_inactive setting must be greater than ignore_older + scan_frequency to make sure that no states are removed while a file is still being harvested. Otherwise, the setting could result in Filebeat resending the full content constantly because clean_inactive removes state for files that are still detected by Filebeat. If a file is updated or appears again, the file is read from the beginning.

The clean_inactive configuration option is useful to reduce the size of the registry file, especially if a large amount of new files are generated every day.

This config option is also useful to prevent Filebeat problems resulting from inode reuse on Linux. For more information, see Inode reuse causes Filebeat to skip lines.

Every time a file is renamed, the file state is updated and the counter for clean_inactive starts at 0 again.

During testing, you might notice that the registry contains state entries that should be removed based on the clean_inactive setting. This happens because Filebeat doesn’t remove the entries until it opens the registry again to read a different file. If you are testing the clean_inactive setting, make sure Filebeat is configured to read from more than one file, or the file state will never be removed from the registry.

`clean_removed`

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When this option is enabled, Filebeat cleans files from the registry if they cannot be found on disk anymore under the last known name. This means also files which were renamed after the harvester was finished will be removed. This option is enabled by default.

If a shared drive disappears for a short period and appears again, all files will be read again from the beginning because the states were removed from the registry file. In such cases, we recommend that you disable the clean_removed option.

You must disable this option if you also disable close_removed.

`backoff.*`

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The backoff options specify how aggressively Filebeat crawls open files for updates. You can use the default values in most cases.

The backoff option defines how long Filebeat waits before checking a file again after EOF is reached. The default is 1s, which means the file is checked every second if new lines were added. This enables near real-time crawling. Every time a new line appears in the file, the backoff value is reset to the initial value. The default is 1s.

`backoff.init`

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The maximum time for Filebeat to wait before checking a file again after EOF is reached. After having backed off multiple times from checking the file, the wait time will never exceed max_backoff regardless of what is specified for backoff_factor. Because it takes a maximum of 10s to read a new line, specifying 10s for max_backoff means that, at the worst, a new line could be added to the log file if Filebeat has backed off multiple times. The default is 10s.

Requirement: Set max_backoff to be greater than or equal to backoff and less than or equal to scan_frequency (backoff <= max_backoff <= scan_frequency). If max_backoff needs to be higher, it is recommended to close the file handler instead and let Filebeat pick up the file again.

`backoff.max`

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`file_identity`

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Different file_identity methods can be configured to suit the environment where you are collecting log messages.

Changing file_identity methods between runs may result in duplicated events in the output.

native: The default behaviour of Filebeat is to differentiate between files using their inodes and device ids.

file_identity.native: ~

path: To identify files based on their paths use this strategy.

Only use this strategy if your log files are rotated to a folder outside of the scope of your input or not at all. Otherwise you end up with duplicated events.

This strategy does not support renaming files. If an input file is renamed, Filebeat will read it again if the new path matches the settings of the input.

file_identity.path: ~

inode_marker: If the device id changes from time to time, you must use this method to distinguish files. This option is not supported on Windows.

Set the location of the marker file the following way:

file_identity.inode_marker.path: /logs/.filebeat-marker

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