Merge pull request #3535 from olehermanse/limits

Added limits to documentation

Author: olehermanse

content/reference/limits.markdown

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+---
+layout: default
+title: Limits
+categories: [Reference, Limits]
+---
+
+There are various limits enforced in CFEngine, for names and values in both policy, web UI, and other places.
+It can sometimes be relevant for both developers and users to know what limits are in place.
+The term limits is used broadly, referring to different kinds of limits (character limits, rate limits, allowed / blocked characters, etc.).
+
+## Limits in policy language and evaluation
+
+**Variable names:** Maximum 1024 characters.
+
+**Variable values (strings):** No explicit maximum, we've tested strings of several megabytes, however this is not recommended for several reasons:
+
+- When strings get excessively long, everything you do with them takes a long time.
+  To test this and give some kind of idea: parsing and storing a ~3MB string in a variable took 25 seconds on the author's laptop.
+- If you want to include these variables in reporting data, they will be truncated.
+  (See below for details).
+- Any time you print such a variable, there will be a lot of output.
+  (And printing this data to file or console is also slow).
+- `cf-agent` will exit if you create variables so large that you run out of memory.
+- Historically, some built-in functions in policy language have truncated strings (usually to around 4K bytes).
+  This is not intended / desirable, we are fixing those, but it might be relevant for you, especially if you use older versions of CFEngine.
+
+For these reasons, we recommend keeping both variable names and values (strings) to less than 1000 bytes.
+If you need more, and you're okay with them being truncated in the reporting data, larger strings should also work well.
+You can, for example, try to stay within 16K, it should not be particularly slow.
+
+## Limits in reporting data
+
+Each entity reported (such as a variable or class), including metadata about it, needs to fit within a 4096 byte network "transaction".
+
+**Variables:** Maximum 4078 bytes combined for namespace, bundle name, variable name, variable value, and tags.
+The last 18 bytes up to 4096 are a timestamp, and the separators added between the fields.
+
+**Classes:** Maximum 4080 bytes combined for class name and tags.
+The last 16 bytes are used for a timestamp and the separators.
+
+## Limits in Web UI and Rest API
+
+**URLs:** The URLs used in settings for LLMs and CFEngine Build projects are limited to 2048 characters.
+
+**Group names:** Maximum 100 characters.
+
+**Passwords:** Maximum 20 characters.
+
+### CMDB / group data / host specific data
+
+**Names:** Maximum 255 characters.
+
+**Values:** Maximum 16 000 characters (16k).
+
+## Limits in CFEngine Build
+
+**Module names:** Maximum 64 characters.
+Lowercase ASCII alphanumericals, starting with a letter, and possible singular dashes in the middle.
+Uppercase letters and other symbols are not permitted.
+
+**Build steps:** Maximum 256 characters.
+
+**Filenames:** Maximum 128 characters.
+Lowercase and uppercase ASCII letters, dots, dashes, and underscores.
+Spaces and other symbols (like slashes, quotes, and semicolons) are not permitted.
+
+<!--
+
+Todos:
+
+Password attempt limits.
+2FA attempt limits.
+
+Namespace name length.
+Bundle name length.
+Qualified name length (namespace:bundle.name).
+-->