PublishReadyToRun configuration for trimmed low-traffic workloads

Direct answer

With TrimMode=partial, only assemblies explicitly marked IsTrimmable are trimmed. Reflection-heavy libraries that are not marked keep their full metadata, so PublishReadyToRun stability risk is low for them. For opted-in assemblies, the trimmer runs before R2R compilation; any reflection-only member removed becomes missing metadata that the precompiled native code may reference at runtime, producing failures such as MissingMethodException.

On Linux, use the portable RID linux-x64 (or linux-arm64) rather than a distro-specific RID. Minor kernel updates preserve the user-space ABI, so R2R compatibility depends on the target glibc version and CPU architecture, not the kernel version. Distro-specific RIDs like ubuntu.22.04-x64 tie the binary to that distro's ABI and reduce portability.

Confirmed behavior and assumptions

These points reflect documented .NET 6+ trimming and R2R behavior:

• Partial trim does not protect opted-in assemblies from reflection breakage; the ILLink trimmer still removes unused members from them.
• R2R native code is generated after trimming, so it can embed references to metadata that the trimmer has already removed.
• linux-x64 images assume glibc; they will not run on musl-based distributions such as Alpine without a separate build.
• Kernel updates rarely break user-space compatibility, but OS upgrades that change glibc can invalidate untested R2R images.

Steps for this case

1. Determine whether the reflection-heavy library is marked IsTrimmable. If it is not, leave it out of trimming concerns and focus on RID choice.
2. If it is opted in, annotate dynamic access paths with DynamicDependency or preserve roots, and enable trim analysis warnings.
3. Publish with a portable RID and self-contained mode so the runtime and R2R images travel together.
4. Run the published output on a clean VM that matches the target glibc version.

Safe publish command

dotnet publish \
  -c Release \
  -r linux-x64 \
  --self-contained true \
  -p:PublishReadyToRun=true \
  -p:TrimMode=partial \
  -p:PublishTrimmed=true

Verification

Confirm the target glibc version on the host (for example, ldd --version or getconf GNU_LIBC_VERSION), then run the application there. Enable trim analysis and confirm there are zero unresolved ILLink warnings for any assembly marked IsTrimmable. Finally, measure cold-start latency with and without R2R under simulated low-traffic conditions to confirm the trade-off is worthwhile.

One diagnostic that changes the recommendation

Is the reflection-heavy library explicitly marked IsTrimmable? If yes, you need preservation attributes and a clean ILLink pass before shipping. If no, partial trim leaves it untouched, and the remaining decision is purely about RID portability and whether R2R's size/memory overhead is justified for your traffic pattern.