# Google Pub/Sub gRPC Starting with version 4.10.0, AxoSyslog can send data to [Google Cloud Pub/Sub]() using its [gRPC interface](). ## Prerequisites * A [Google Pub/Sub subscription](). * An [IAM service account]() that AxoSyslog uses for authentication. * A Google Cloud project that has the Pub/Sub API enabled. For details, see the [Google Pub/Sub tutorial](). ## Configuration To configure AxoSyslog, you’ll need the name of the project and the topic where you want to send your data. Example configuration: ``` destination d_pubsub_grpc { google-pubsub-grpc( project("my_project") topic($topic) data($MESSAGE) attributes( timestamp => $S_ISODATE, host => $HOST, ) workers(4) batch-timeout(1000) # ms batch-lines(1000) ); }; ``` You can change the default endpoint using [`service_endpoint()`](../../docs/axosyslog-core/chapter-destinations/google-pubsub-grpc/index.md#service_endpoint). ## Options The following options are specific to the `google-pubsub-grpc()` destination. ## attributes() | ---|--- Type: | string Default: | `"--scope rfc5424,all-nv-pairs --exclude MESSAGE"` _Description:_ A JSON object representing key-value pairs for the Pub/Sub Event, formatted as [AxoSyslog value-pairs](../../docs/axosyslog-core/chapter-concepts/concepts-value-pairs/option-value-pairs/index.md). By default, the destination sends the RFC5424 fields as attributes. If you want to send different fields, override the default template. By default, the message part is sent in the [`data()`](../../docs/axosyslog-core/chapter-destinations/google-pubsub-grpc/index.md#data) option. If you want to dynamically create the `data()` and `attributes()` part of the message, use the `protovar()` attribute. ## auth() Options for cloud-related authentication. Currently only the [GCP Service Account authentication]() is supported. Specify the JSON file storing the key to the service account like this: ``` auth( service-account( key("/path/to/service-account-key.json") ) ) ``` #### service-account() Authenticate to a service account using Service Account Key-Based Authentication. This method works both inside and outside GCP It uses a [service account key]() generated and downloaded through the GCP IAM & Admin console. The long-term service account key is used to generate short-term tokens for authentication (also called [self-signed JWT]()). ##### audience() | ---|--- Type: | string Default: | Note * When using the `google-pubsub()` destination, the `audience()` option is set to `https://pubsub.googleapis.com/google.pubsub.v1.Publisher`. Don’t change it. * When using the `google-pubsub()-grpc` destination, you don’t need to set the `audience()` option because the underlying gRPC API recognizes it automatically. * You cannot use `audience()` and `scope()` together. ##### key() | ---|--- Type: | string (path) Default: | Path to the service account key. ##### scope() | ---|--- Type: | string Default: | Available in AxoSyslog version 4.15 and later. URL for a scope claim for authentication [instead of audience](). For example: ``` ... cloud-auth( gcp( service-account( key("/path/to/secret.json") scope("https://www.googleapis.com/auth/example-scope") ) ) ) ``` Note You cannot use `audience()` and `scope()` together. ##### token-validity-duration() | ---|--- Type: | integer (seconds) Default: | `3600` #### user-managed-service-account() Available in AxoSyslog version 4.6 and later. Note The `user-managed-service-account()` method is only available for VMs running within GCP. Authenticate to a [user-managed service account]() of a GCP virtual machine using the VM Metadata Server Method. AxoSyslog interacts with the internal GCP metadata server, which provides an OAuth2 token for authentication. You can attach the [default service accounts]() as well. ##### metadata-url() | ---|--- Type: | string Default: | `http://metadata.google.internal/computeMetadata/v1/instance/service-accounts` The URL of the metadata server. When specifying the port, use the `URL:port` format. ##### name() | ---|--- Type: | string Default: | `default` Name of the service account to use. ## batch-bytes() | ---|--- Accepted values: | number [bytes] Default: | none _Description:_ Sets the maximum size of payload in a batch. If the size of the messages reaches this value, AxoSyslog sends the batch to the destination even if the number of messages is less than the value of the `batch-lines()` option. Note that if the `batch-timeout()` option is enabled and the queue becomes empty, AxoSyslog flushes the messages only if `batch-timeout()` expires, or the batch reaches the limit set in `batch-bytes()`. Available in AxoSyslog version 3.19 and later. ## batch-idle-timeout() | ---|--- Type: | time in milliseconds Default: | `0` (disabled) Available in AxoSyslog 4.24 and later. _Description:_ `batch-idle-timeout()` measures the elapsed time since the last message was added to the batch (`batch-timeout()` defines the maximum time used to collect a batch, starting from the first message). If either `batch-idle-timeout()` or `batch-timeout()` expires, AxoSyslog closes and sends the batch. ## batch-lines() | ---|--- Type: | number Default: | 0 _Description:_ Specifies how many lines are flushed to a destination in one batch. The AxoSyslog application waits for this number of lines to accumulate and sends them off in a single batch. Increasing this number increases throughput as more messages are sent in a single batch, but also increases message latency. To disable `batch-lines()`, set it to `0`. For example, if you set `batch-lines()` to 100, AxoSyslog waits for 100 messages. If the `batch-timeout()` option is disabled, the AxoSyslog application flushes the messages if it has sent `batch-lines()` number of messages, or the queue became empty. If you stop or reload AxoSyslog or in case of network sources, the connection with the client is closed, AxoSyslog automatically sends the unsent messages to the destination. Note that if the `batch-timeout()` option is enabled and the queue becomes empty, AxoSyslog flushes the messages only if `batch-timeout()` expires, or the batch reaches the limit set in `batch-lines()`. For optimal performance, make sure that the AxoSyslog source that feeds messages to this destination is configured properly: the value of the `log-iw-size() / max-connections()` of the source must be higher than the `batch-lines() * workers()` of the destination. Otherwise, the size of the batches cannot reach the `batch-lines()` limit. ## batch-timeout() | ---|--- Type: | time in milliseconds Default: | `-1` (disabled) _Description:_ Specifies the time AxoSyslog waits for lines to accumulate in the output buffer. The AxoSyslog application sends batches to the destinations evenly. The timer starts when the first message arrives to the buffer, so if only few messages arrive, AxoSyslog sends messages to the destination at most once every `batch-timeout()` milliseconds. ## channel-args() | ---|--- Type: | arrow list Default: | - _Description:_ The `channel-args()` option is available in gRPC-based drivers. It accepts name-value pairs and sets channel arguments defined in the [GRPC Core library documentation](). For example: ``` channel-args( "grpc.loadreporting" => 1 "grpc.minimal_stack" => 0 ) ``` ## compression() | ---|--- Type: | boolean Default: | `no` Available in AxoSyslog version 4.5.0 and later. _Description:_ Enables compression in gRPC requests. Although gRPC supports various compression methods, currently only deflate is supported (which is basically the same as gzip). ## data() | ---|--- Type: | string/template Default: | `"${MESSAGE}"` _Description:_ The template to use as the data part of the Google Pub/Sub message. ## disk-buffer() _Description:_ This option enables putting outgoing messages into the disk buffer of the destination to avoid message loss in case of a system failure on the destination side. It has the following options: ### capacity-bytes() Type: | number (bytes) ---|--- Default: | 1MiB _Description:_ This is a required option. The maximum size of the disk-buffer in bytes. The minimum value is `1048576` bytes. If you set a smaller value, the minimum value will be used automatically. It replaces the old `log-disk-fifo-size()` option. In AxoSyslog version 4.2 and earlier, this option was called `disk-buf-size()`. ### compaction() Type: | yes/no ---|--- Default: | no _Description:_ If set to `yes`, AxoSyslog prunes the unused space in the LogMessage representation, making the disk queue size smaller at the cost of some CPU time. Setting the `compaction()` argument to `yes` is recommended when numerous name-value pairs are unset during processing, or when the same names are set multiple times. Note Simply unsetting these name-value pairs by using the `unset()` rewrite operation is not enough, as due to performance reasons that help when AxoSyslog is CPU bound, the internal representation of a `LogMessage` will not release the memory associated with these name-value pairs. In some cases, however, the size of this overhead becomes significant (the raw message size can grow up to four times its original size), which unnecessarily increases the disk queue file size. For these cases, the compaction will drop `unset` values, making the `LogMessage` representation smaller at the cost of some CPU time required to perform compaction. ### dir() Type: | string ---|--- Default: | N/A _Description:_ Defines the folder where the disk-buffer files are stored. Warning When creating a new `dir()` option for a disk buffer, or modifying an existing one, make sure you delete the persist file. AxoSyslog creates disk-buffer files based on the path recorded in the persist file. Therefore, if the persist file is not deleted after modifying the `dir()` option, then following a restart, AxoSyslog will look for or create disk-buffer files in their old location. To ensure that AxoSyslog uses the new `dir()` setting, the persist file must not contain any information about the destinations which the disk-buffer file in question belongs to. Note If the `dir()` path provided by the user does not exist, AxoSyslog creates the path with the same permission as the running instance. ### flow-control-window-bytes() Type: | number (bytes) ---|--- Default: | 163840000 _Description:_ Use this option if the option `reliable()` is set to `yes`. This option contains the size of the messages in bytes that is used in the memory part of the disk buffer. It replaces the old `log-fifo-size()` option. It does not inherit the value of the global `log-fifo-size()` option, even if it is provided. Note that this option will be ignored if the option `reliable()` is set to `no`. In AxoSyslog version 4.2 and earlier, this option was called `mem-buf-size()`. ### flow-control-window-size() Type: | number(messages) ---|--- Default: | 10000 _Description:_ Use this option if the option `reliable()` is set to `no`. This option contains the number of messages stored in overflow queue. It replaces the old `log-fifo-size()` option. It inherits the value of the global `log-fifo-size()` option if provided. If it is not provided, the default value is `10000` messages. Note that this option will be ignored if the option `reliable()` is set to `yes`. In AxoSyslog version 4.2 and earlier, this option was called `mem-buf-length()`. ### front-cache-size() Type: | number(messages) ---|--- Default: | 1000 _Description:_ The number of messages stored in the output buffer of the destination. Note that if you change the value of this option and the disk-buffer already exists, the change will take effect when the disk-buffer becomes empty. Options `reliable()` and `capacity-bytes()` are required options. In AxoSyslog version 4.2 and earlier, this option was called `qout-size()`. ### prealloc() Type: | yes/no ---|--- Default: | no _Description:_ By default, AxoSyslog doesn’t reserve the disk space for the disk-buffer file, since in a properly configured and sized environment the disk-buffer is practically empty, so a large preallocated disk-buffer file is just a waste of disk space. But a preallocated buffer can prevent other data from using the intended buffer space (and elicit a warning from the OS if disk space is low), preventing message loss if the buffer is actually needed. To avoid this problem, when using AxoSyslog 4.0 or later, you can preallocate the space for your disk-buffer files by setting `prealloc(yes)`. In addition to making sure that the required disk space is available when needed, preallocated disk-buffer files provide radically better (3-4x) performance as well: in case of an outage the amount of messages stored in the disk-buffer is continuously growing, and using large continuous files is faster, than constantly waiting on a file to change its size. If you are running AxoSyslog on a dedicated host (always recommended for any high-volume settings), use `prealloc(yes)`. Available in AxoSyslog 4.0 and later. ### reliable() Type: | yes/no ---|--- Default: | no _Description:_ If set to `yes`, AxoSyslog cannot lose logs in case of reload/restart, unreachable destination or AxoSyslog crash. This solution provides a slower, but reliable disk-buffer option. It is created and initialized at startup and gradually grows as new messages arrive. If set to `no`, the normal disk-buffer will be used. This provides a faster, but less reliable disk-buffer option. Warning Hazard of data loss! If you change the value of `reliable()` option when there are messages in the disk-buffer, the messages stored in the disk-buffer will be lost. ### truncate-size-ratio() Type: | number((between 0 and 1)) ---|--- Default: | 1 (do not truncate) _Description:_ Limits the truncation of the disk-buffer file. Truncating the disk-buffer file can slow down the disk IO operations, but it saves disk space. By default, AxoSyslog version 4.0 and later doesn’t truncate disk-buffer files by default (`truncate-size-ratio(1)`). Earlier versions freed the disk-space when at least 10% of the disk-buffer file could be freed (`truncate-size-ratio(0.1)`). AxoSyslog only truncates the file if the possible disk gain is more than `truncate-size-ratio()` times `capacity-bytes()`. * Smaller values free disk space quicker. * Larger ratios result in better performance. If you want to avoid performance fluctuations: * use `truncate-size-ratio(1)` (never truncate), or * use `prealloc(yes)` to reserve the entire size of the disk-buffer on disk. Warning Axoflow does not recommend you to change `truncate-size-ratio()`. Only change its value if you understand the performance implications of doing so. ### Example: Examples for using disk-buffer() In the following case reliable disk-buffer() is used. ``` destination d_demo { network( "127.0.0.1" port(3333) disk-buffer( flow-control-window-bytes(10000) capacity-bytes(2000000) reliable(yes) dir("/tmp/disk-buffer") ) ); }; ``` In the following case normal disk-buffer() is used. ``` destination d_demo { network( "127.0.0.1" port(3333) disk-buffer( flow-control-window-size(10000) capacity-bytes(2000000) reliable(no) dir("/tmp/disk-buffer") ) ); }; ``` ## frac-digits() | ---|--- Type: | number Default: | 0 _Description:_ The AxoSyslog application can store fractions of a second in the timestamps according to the ISO8601 format. The `frac-digits()` parameter specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received. Note The AxoSyslog application can add the fractions to non-ISO8601 timestamps as well. Note As AxoSyslog is precise up to the microsecond, when the `frac-digits()` option is set to a value higher than 6, AxoSyslog will truncate the fraction seconds in the timestamps after 6 digits. ## headers() | ---|--- Type: | arrow list Default: | empty Available in AxoSyslog 4.8 and later. _Description:_ Adds custom gRPC headers to each RPC call. Version 4.8 supported only static header names and values. For example: ``` headers( "organization" => "Axoflow" "stream-name" => "axo-stream" ) ``` Starting with version 4.9, you can use templates and macros in the header values. ``` headers( "organization" => "Axoflow" "stream-name" => "${HOST}" ) ``` ## hook-commands() _Description:_ This option makes it possible to execute external programs when the relevant driver is initialized or torn down. The `hook-commands()` can be used with all source and destination drivers with the exception of the `usertty()` and `internal()` drivers. Note The AxoSyslog application must be able to start and restart the external program, and have the necessary permissions to do so. For example, if your host is running AppArmor or SELinux, you might have to modify your AppArmor or SELinux configuration to enable AxoSyslog to execute external applications. ### Using `hook-commands()` when AxoSyslog starts or stops To execute an external program when AxoSyslog starts or stops, use the following options: #### `startup()` Type: | string ---|--- Default: | N/A _Description:_ Defines the external program that is executed as AxoSyslog starts. #### `shutdown()` Type: | string ---|--- Default: | N/A _Description:_ Defines the external program that is executed as AxoSyslog stops. ### Using the hook-commands() when AxoSyslog reloads To execute an external program when the AxoSyslog configuration is initiated or torn down, for example, on startup/shutdown or during a AxoSyslog reload, use the following options: #### `setup()` Type: | string ---|--- Default: | N/A _Description:_ Defines an external program that is executed when the AxoSyslog configuration is initiated, for example, on startup or during a AxoSyslog reload. #### `teardown()` Type: | string ---|--- Default: | N/A _Description:_ Defines an external program that is executed when the AxoSyslog configuration is stopped or torn down, for example, on shutdown or during a AxoSyslog reload. ### Example: Using hook-commands() with a network source In the following example, the `hook-commands()` is used with the `network()` driver and it opens an [iptables]( "https://en.wikipedia.org/wiki/Iptables") port automatically as AxoSyslog is started/stopped. The assumption in this example is that the `LOGCHAIN` chain is part of a larger ruleset that routes traffic to it. Whenever the AxoSyslog created rule is there, packets can flow, otherwise the port is closed. ``` source { network(transport(udp) hook-commands(           startup("iptables -I LOGCHAIN 1 -p udp --dport 514 -j ACCEPT")           shutdown("iptables -D LOGCHAIN 1")         )      ); }; ``` ## keep-alive() Configures how AxoSyslog sends [gRPC keepalive pings](). ### max-pings-without-data() | ---|--- Type: | integer Default: | _Description:_ The maximum number of gRPC pings that can be sent when there is no data/header frame to be sent. AxoSyslog won’t send any pings after this limit. Set it to 0 disable this restriction and keep sending pings. ### time() | ---|--- Type: | number [milliseconds] Default: | _Description:_ The period (in milliseconds) after which AxoSyslog sends a gRPC keepalive ping. ### timeout() | ---|--- Type: | number [milliseconds] Default: | 10 _Description:_ The time (in milliseconds) AxoSyslog waits for an acknowledgement. ## local-time-zone() | ---|--- Type: | name of the timezone, or the timezone offset Default: | The local timezone. _Description:_ Sets the timezone used when expanding filename and tablename templates. The timezone can be specified by using the name, for example, `time-zone("Europe/Budapest")`), or as the timezone offset in +/-HH:MM format, for example, `+01:00`). On Linux and UNIX platforms, the valid timezone names are listed under the `/usr/share/zoneinfo` directory. ## log-fifo-size() | ---|--- Type: | number Default: | Use global setting. _Description:_ The number of messages that the output queue can store. ## on-error() Type: | One of: `drop-message`, `drop-property`, `fallback-to-string`, `silently-drop-message`, `silently-drop-property`, `silently-fallback-to-string` ---|--- Default: | Use the global setting (which defaults to `drop-message`) _Description:_ Controls what happens when type-casting fails and AxoSyslog cannot convert some data to the specified type. By default, AxoSyslog drops the entire message and logs the error. Currently the `value-pairs()` option uses the settings of `on-error()`. * `drop-message`: Drop the entire message and log an error message to the `internal()` source. This is the default behavior of AxoSyslog. * `drop-property`: Omit the affected property (macro, template, or message-field) from the log message and log an error message to the `internal()` source. * `fallback-to-string`: Convert the property to string and log an error message to the `internal()` source. * `silently-drop-message`: Drop the entire message silently, without logging the error. * `silently-drop-property`: Omit the affected property (macro, template, or message-field) silently, without logging the error. * `silently-fallback-to-string`: Convert the property to string silently, without logging the error. ## persist-name() | ---|--- Type: | string Default: | N/A _Description:_ If you receive the following error message during AxoSyslog startup, set the `persist-name()` option of the duplicate drivers: ``` Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down. ``` This error happens if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the `persist-name()` of the drivers to a custom string, for example, `persist-name("example-persist-name1")`. ## project() | ---|--- Type: | string/template Default: | - _Description:_ The ID of the Google Cloud project where AxoSyslog sends the data. The Pub/Sub API must be enabled for the project. ## proto-var() | ---|--- Type: | template Default: | - _Description:_ An alternative to using [`attributes()`](../../docs/axosyslog-core/chapter-destinations/google-pubsub-grpc/index.md#attributes) and [`data()`](../../docs/axosyslog-core/chapter-destinations/google-pubsub-grpc/index.md#data). The advantage of `protovar()` is that the number of attributes it sends to the destination can vary between the messages, it doesn’t have to be constant. That’s useful is you’re dynamically building your messages using [FilterX](../../docs/axosyslog-core/filterx/index.md). ## response-action() | ---|--- Type: | arrow list Default: | Depends on the driver Available in AxoSyslog version 4.11.0 and later. _Description:_ Fine-tunes how AxoSyslog behaves in case of different gRPC results. You can assign specific actions to the different gRPC results, for example: ``` response-action( not-found => disconnect unavailable => drop ) ``` The following gRPC results are supported: * `aborted` * `already-exists` * `cancelled` * `data-loss` * `deadline-exceeded` * `failed-precondition` * `internal` * `invalid-argument` * `not-found` * `ok` * `out-of-range` * `permission-denied` * `resource-exhausted` * `unauthenticated` * `unavailable` * `unknown` * `unimplemented` The following actions are available: * `disconnect` * `drop` * `retry` * `success` ## retries() | ---|--- Type: | number (of attempts) Default: | 3 _Description:_ If AxoSyslog cannot send a message, it will try again until the number of attempts reaches `retries()`. If the number of attempts reaches `retries()`, AxoSyslog will wait for `time-reopen()` time, then tries sending the message again. ## send-time-zone() | ---|--- Accepted values: | name of the timezone, or the timezone offset Default: | local timezone _Description:_ Specifies the time zone associated with the messages sent by `syslog-ng`, if not specified otherwise in the message or in the destination driver. For details, see [Timezones and daylight saving](../../docs/axosyslog-core/chapter-concepts/timezone-handling/index.md). The timezone can be specified by using the name, for example, `time-zone("Europe/Budapest")`), or as the timezone offset in +/-HH:MM format, for example, `+01:00`). On Linux and UNIX platforms, the valid timezone names are listed under the `/usr/share/zoneinfo` directory. ## service_endpoint() | ---|--- Type: | string Default: | `pubsub.googleapis.com:443` The service endpoint for the Pub/Sub API where AxoSyslog sends the data. For a list of locational endpoints, see the [official Pub/Sub APIs documentation](). ## template-escape() | ---|--- Type: | yes or no Default: | no _Description:_ Turns on escaping for the `'`, `"`, and backspace characters in templated output files. This is useful for generating SQL statements and quoting string contents so that parts of the log message are not interpreted as commands to the SQL server. > Note: Starting with AxoSyslog version 4.5, `template-escape(yes)` escapes the top-level template function in case of nested template functions. ## throttle() | ---|--- Type: | number Default: | 0 _Description:_ Sets the maximum number of messages sent to the destination per second. Use this output-rate-limiting functionality only when using disk-buffer as well to avoid the risk of losing messages. Specifying `0` or a lower value sets the output limit to unlimited. ## time-reopen() | ---|--- Accepted values: | number [seconds] Default: | 60 _Description:_ The time to wait in seconds before a dead connection is reestablished. ## time-zone() | ---|--- Type: | name of the timezone, or the timezone offset Default: | unspecified _Description:_ Convert timestamps to the timezone specified by this option. If this option is not set, then the original timezone information in the message is used. Converting the timezone changes the values of all date-related macros derived from the timestamp, for example, `HOUR`. For the complete list of such macros, see [Date-related macros](../../docs/axosyslog-core/chapter-manipulating-messages/customizing-message-format/date-macros/index.md). The timezone can be specified by using the name, for example, `time-zone("Europe/Budapest")`), or as the timezone offset in +/-HH:MM format, for example, `+01:00`). On Linux and UNIX platforms, the valid timezone names are listed under the `/usr/share/zoneinfo` directory. ## topic() | ---|--- Type: | string/template Default: | - _Description:_ The name of the Google Pub/Sub topic where AxoSyslog sends the data. ## ts-format() | ---|--- Type: | rfc3164, bsd, rfc3339, iso Default: | rfc3164 _Description:_ Override the global timestamp format (set in the global `ts-format()` parameter) for the specific destination. For details, see [ts-format()](../../docs/axosyslog-core/chapter-global-options/reference-options/index.md). Note This option applies only to file and file-like destinations. Destinations that use specific protocols (for example, `network()`, or `syslog()`) ignore this option. For protocol-like destinations, use a template locally in the destination, or use the [proto-template](../../docs/axosyslog-core/chapter-global-options/reference-options/index.md) option. ## url() | ---|--- Type: | string Default: | - _Description:_ An alias for [`service_endpoint`](../../docs/axosyslog-core/chapter-destinations/google-pubsub-grpc/index.md#service-endpoint). ## worker-partition-autoscaling() | ---|--- Type: | `yes`, `no` Default: | `no` Available in version 4.21 and later. When using `worker-partition-key()` to categorize messages into different batches, the messages are hashed into workers by default. This prevents distributing across workers based on load. Setting `worker-partition-autoscaling(yes)` uses a 1-minute statistic to distribute high-traffic partitions among multiple workers, allowing each worker to maximize its batch size. When using `worker-partition-autoscaling(yes)`, set the number of `workers()` to higher than the expected number of partitions. ## worker-partition-buckets() | ---|--- Type: | template Default: | _Description:_ The `worker-partition-buckets()` option determines the number of worker threads used for the `worker-partition-key()`. Note that the number set by `worker-partition-buckets()` should be lower than the number of `workers()`. ## worker-partition-key() | ---|--- Type: | template Default: | _Description:_ The `worker-partition-key()` option specifies a template: messages that expand the template to the same value are mapped to the same partition. When batching is enabled and multiple workers are configured, it’s important to add only those messages to a batch which generate identical URLs. To achieve this, set the `worker-partition-key()` option with a template that contains all the templates used in the `url()` option, otherwise messages will be mixed. For example, you can partition messages based on the destination host: ``` worker-partition-key("$HOST") ``` ## workers() | ---|--- Type: | integer Default: | 1 _Description:_ Specifies the number of worker threads (at least 1) that AxoSyslog uses to send messages to the server. Increasing the number of worker threads can drastically improve the performance of the destination. Warning `Hazard of data loss.` When you use more than one worker threads together with disk-based buffering, AxoSyslog creates a separate disk buffer for each worker thread. This means that decreasing the number of workers can result in losing data currently stored in the disk buffer files. Do not decrease the number of workers when the disk buffer files are in use. Last modified March 20, 2026: [Adds batch-idle-timeout to related destinations (cc2472e)]()