76 lines
3 KiB
Markdown
76 lines
3 KiB
Markdown
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# URL-Based Config Behavior
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## Objective
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Define the retry and reload behavior of remote URLs that are passed as config to
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Telegraf. In terms of retry, currently Telegraf will attempt to load a remote
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URL three times and then exit. In terms of reload, Telegraf does not have the
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capability to reload remote URL based configs. This spec seeks to allow for
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options for the user to further these capabilities.
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## Keywords
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config, error, retry, reload
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## Overview
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Telegraf allows for loading configurations from local files, directories, and
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files via a URL. In order to allow situations where a configuration file is not
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yet available or due to a flaky network, the first proposal is to introduce a
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new CLI flag: `--url-config-retry-attempts`. This flag would continue to default
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to three and would specify the number of retries to attempt to get a remote URL
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during the initial startup of Telegraf.
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```sh
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--config-url-retry-attempts=3 Number of times to attempt to obtain a remote
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configuration via a URL during startup. Set to
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-1 for unlimited attempts.
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```
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These attempts would block Telegraf from starting up completely until success or
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until we have run out of attempts and exit.
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Once Telegraf is up and running, users can use the `--watch` flag to enable
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watching local files for changes and if/when changes are made, then reload
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Telegraf with the new configuration. For remote URLs, I propose a new CLI flag:
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`--url-config-check-interval`. This flag would set an internal timer that when
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it goes off, would check for an update to a remote URL file.
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```sh
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--config-url-watch-interval=0s Time duration to check for updates to URL based
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configuration files. Disabled by default.
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```
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At each interval, Telegraf would send an HTTP HEAD request to the configuration
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URL, here is an example curl HEAD request and output:
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```sh
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$ curl --head http://localhost:8000/config.toml
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HTTP/1.0 200 OK
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Server: SimpleHTTP/0.6 Python/3.12.3
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Date: Mon, 29 Apr 2024 18:18:56 GMT
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Content-type: application/octet-stream
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Content-Length: 1336
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Last-Modified: Mon, 29 Apr 2024 11:44:19 GMT
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```
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The proposal then is to store the last-modified value when we first obtain the
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file and compare the value at each interval. No need to parse the value, just
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store the raw string. If there is a difference, trigger a reload.
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If anything other than 2xx response code is returned from the HEAD request,
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Telegraf would print a warning message and retry at the next interval. Telegraf
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will continue to run the existing configuration with no change.
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If the value of last-modified is empty, while very unlikely, then Telegraf would
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ignore this configuration file. Telegraf will print a warning message once about
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the missing field.
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## Relevant Issues
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* Configuration capabilities to retry for loading config via URL #[8854][]
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* Telegraf reloads URL-based/remote config on a specified interval #[8730][]
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[8854]: https://github.com/influxdata/telegraf/issues/8854
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[8730]: https://github.com/influxdata/telegraf/issues/8730
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