[SVLS-9100] fix(install): Function App slot workaround + install templates (#455) by Lewis-E · Pull Request #457 · DataDog/datadog-aas-extension

Lewis-E · 2026-05-22T17:30:12Z

Summary

Addresses #455 — intermittent MoveDirectory failures when installing the Datadog extension on Azure Function App deployment slots.

Root cause: The Functions runtime holds file locks on C:\home\SiteExtensions\ after code deployment. If a site extension ARM deployment runs while those handles are open, Kudu's MoveDirectory step fails. This does not affect Web Apps.

Fix: Set WEBSITE_PRIVATE_EXTENSIONS=0 as a sticky slot setting. This prevents the Functions runtime from loading private site extensions on that slot (releasing the file locks). Because the setting is sticky, it stays on the staging slot after swaps and never affects production.

Changes

`install-templates/` (renamed from `ARM/`)

install-web-app.{json,bicep} — Web App install templates
install-web-app-slot.{json,bicep} — Web App deployment slot templates
install-function-app-slot.{json,bicep} — New: Function App slot templates with WEBSITE_PRIVATE_EXTENSIONS=0 sticky setting + slotConfigNames resource, dependsOn ordering to ensure setting is applied before extension install
All templates versioned (metadata.version in JSON, // Version: in Bicep) to allow comparison against docs inline snippets

PowerShell scripts

install-latest-extension.ps1 v2.0.0: adds -SlotName parameter; when provided against a Function App, automatically applies WEBSITE_PRIVATE_EXTENSIONS=0 as a sticky slot setting.
update-all-site-extensions.ps1 v2.0.0: adds -IncludeSlots flag to enumerate and update deployment slots across a resource group

`README.md`

Adds "In-repo resources" section pointing at install-templates/ and management-scripts/extension/

Companion PR

Must be merged alongside: DataDog/documentation#36956

The docs PR updates the ARM/ → install-templates/ link and adds the new azure_functions/dotnet_extension.md page. The rename here will break the existing docs link until both land.

Test plan

Verify JSON templates are valid (python3 -m json.tool)
Verify Bicep templates compile (az bicep build)
https://github.com/DataDog/serverless-init-self-monitoring/pull/415 demonstrates a function app deploy with fix in place
Verify install-latest-extension.ps1 with -SlotName on a Web App (no Function App branch taken)
Verify install-latest-extension.ps1 with -SlotName on a Function App (sticky setting applied)
Verify install-latest-extension.ps1 without -SlotName (behavior unchanged)
Verify update-all-site-extensions.ps1 without -IncludeSlots (behavior unchanged)

🤖 Generated with Claude Code

…cenarios (#455) Addresses intermittent MoveDirectory failures when installing the Datadog extension on Azure Function App deployment slots. The Functions runtime holds file locks on C:\home\SiteExtensions\ after code deployment; setting WEBSITE_PRIVATE_EXTENSIONS=0 as a sticky slot setting prevents this. Changes: - Rename ARM/ → install-templates/ (docs link update coordinated in companion PR) - Add install-templates/install-web-app.{json,bicep} — Web App templates - Add install-templates/install-web-app-slot.{json,bicep} — Web App slot templates - Add install-templates/install-function-app-slot.{json,bicep} — Function App slot templates with WEBSITE_PRIVATE_EXTENSIONS=0 sticky setting workaround - All templates versioned (metadata.version / // Version comment) for doc comparison - management-scripts/extension/install-latest-extension.ps1 v2.0.0: - Add -SlotName parameter for slot targeting - Auto-detect Function Apps and apply sticky WEBSITE_PRIVATE_EXTENSIONS=0 setting before install when -SlotName is provided - management-scripts/extension/update-all-site-extensions.ps1 v2.0.0: - Add -IncludeSlots flag to enumerate and update deployment slots Co-Authored-By: Claude Sonnet 4.6 (1M context) <[email protected]>

…cleanup - install-function-app-slot: add required existingStickyAppSettingNames param so slotConfigNames uses union() instead of a hard-coded single-entry list; deployment now fails fast rather than silently de-stickying existing settings - install-latest-extension.ps1: remove redundant --settings call before --slot-settings (latter is sufficient and already additive) - update-all-site-extensions.ps1: remove dead $slotExtensionManage in slot loop; add "not found" log for slots to match webapp loop behaviour - All templates: normalize ddService/ddVersion defaults to '' (was 'my-service' / '0.0.0' in web-app templates, '' in function-app template) - README: replace buried Note with fetch-before-deploy instructions and parameterised deploy examples Co-Authored-By: Claude Sonnet 4.6 (1M context) <[email protected]>

ava-silver · 2026-05-27T15:29:44Z

I am slightly wary of having another docs-like copy to maintain, are y'all expecting to maintain these or would that be something the onboarding team would need to do?

My plan is to use this as the test case for an auto-docs-sync AI tool, where if you update this side, it also opens a PR to update the documentation and notifies you accordingly. The work should fall on us, and I want to automate it as much as possible. This is a good test case for the similarity, since we already had a template duplicate here.

ava-silver · 2026-05-27T16:38:10Z

how much do we feel the need to have both bicep/ARM, or would it be okay to just use bicep and give people the command to compile it to ARM?

So I was thinking of this page: https://docs.datadoghq.com/serverless/azure_app_service/windows_code?tab=armtemplate where we have both ARM and Bicep examples. I was trying to be consistent, but I would personally be fine with just bicep. Thoughts on the value of consistency?

Either way we'll have consistency problems, just do we want to keep the same style as the docs, or have to maintain consistency between the bicep/arm forms. Given this isn't being treated as docs (its live code), i do think just having bicep is fine but i'm not fierce on it

ava-silver

Automated review by Claude

Stop clears file locks directly; the sticky setting then persists to ARM and takes effect on the subsequent start — no redundant async recycle. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

… duplication Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

@Args

@Args splats the automatic variable (empty); @cmdArgs splats the constructed argument list. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Mirrors the non-slot branch: when -ExtensionVersion is requested and the slot is already at that version, log and break instead of proceeding through stop/install/start. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

… $baseApiUrl -like on an array returns all matches; indexing to [0] ensures a scalar string is used in URL construction and -replace. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Lewis-E mentioned this pull request May 22, 2026

[SVLS-9100] docs(aas): Function App slot install guidance and MoveDirectory troubleshooting DataDog/documentation#36956

Merged

3 tasks

Lewis-E changed the title ~~fix(install): Function App slot workaround + install templates (#455)~~ [SVLS-9100] fix(install): Function App slot workaround + install templates (#455) May 22, 2026

Lewis-E force-pushed the worktree-issue-455-functionapp-install branch from 9f33c3b to e94e935 Compare May 22, 2026 18:42

Lewis-E linked an issue May 22, 2026 that may be closed by this pull request

[BUG]: Applying the DataDogSiteExtension sometimes fails on an Azure Functions Windows Application #455

Closed

Lewis-E marked this pull request as ready for review May 22, 2026 18:44

Lewis-E requested review from a team as code owners May 22, 2026 18:44

Lewis-E requested review from Chronobreak and removed request for a team May 22, 2026 18:44

ava-silver reviewed May 27, 2026

View reviewed changes

Lewis-E and others added 6 commits May 28, 2026 10:13

Fix extra baseAPiUrl call, use of functionAppName

acf6c8b

fix(install): apply WEBSITE_PRIVATE_EXTENSIONS=0 after stop, not before

62d067f

Stop clears file locks directly; the sticky setting then persists to ARM and takes effect on the subsequent start — no redundant async recycle. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

refactor(install): extract Set-AppSetting helper to remove 6x if/else…

447f7b3

… duplication Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(install): fix Set-AppSetting splat to use @cmdArgs not @Args

6faecdd

@Args splats the automatic variable (empty); @cmdArgs splats the constructed argument list. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(update-all): add version idempotency check to slot path

5638334

Mirrors the non-slot branch: when -ExtensionVersion is requested and the slot is already at that version, log and break instead of proceeding through stop/install/start. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

fix(scripts): guard enabledHostNames filter with [0] to prevent array…

7ad67b2

… $baseApiUrl -like on an array returns all matches; indexing to [0] ensures a scalar string is used in URL construction and -replace. Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

Lewis-E requested a review from ava-silver May 28, 2026 18:23

Chronobreak approved these changes Jun 1, 2026

View reviewed changes

Lewis-E merged commit 10afaf0 into master Jun 1, 2026
3 checks passed

Lewis-E deleted the worktree-issue-455-functionapp-install branch June 1, 2026 16:52

ava-silver mentioned this pull request Jun 23, 2026

[SVLS-9186] add Windows Function App support to aas instrument DataDog/datadog-ci#2357

Merged

1 task

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[SVLS-9100] fix(install): Function App slot workaround + install templates (#455)#457

[SVLS-9100] fix(install): Function App slot workaround + install templates (#455)#457
Lewis-E merged 8 commits into
masterfrom
worktree-issue-455-functionapp-install

Lewis-E commented May 22, 2026 •

edited

Loading

Uh oh!

ava-silver May 27, 2026

Uh oh!

Lewis-E May 27, 2026 •

edited

Loading

Uh oh!

Uh oh!

Uh oh!

Uh oh!

ava-silver May 27, 2026

Uh oh!

Lewis-E May 27, 2026

Uh oh!

ava-silver Jun 1, 2026

Uh oh!

ava-silver left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

Lewis-E commented May 22, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Changes

install-templates/ (renamed from ARM/)

PowerShell scripts

README.md

Companion PR

Test plan

Uh oh!

ava-silver May 27, 2026

Choose a reason for hiding this comment

Uh oh!

Lewis-E May 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

ava-silver May 27, 2026

Choose a reason for hiding this comment

Uh oh!

Lewis-E May 27, 2026

Choose a reason for hiding this comment

Uh oh!

ava-silver Jun 1, 2026

Choose a reason for hiding this comment

Uh oh!

ava-silver left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Lewis-E commented May 22, 2026 •

edited

Loading

`install-templates/` (renamed from `ARM/`)

`README.md`

Lewis-E May 27, 2026 •

edited

Loading