Maven Wagon HTTP Provider Retry Settings for Artifact Deployment

Answer

Enabling <retryCount> in the Maven Wagon HTTP provider does not guarantee that retries are safe. Safety depends entirely on whether the target repository treats HTTP PUT as an idempotent operation (i.e., it overwrites an existing resource with the same URL). If the repository is idempotent, retries will simply re-upload the same file and replace the previous upload, causing no duplicate entries. If the repository treats PUT as a create-only operation (e.g., a plain directory-based layout or a simple HTTP server that stores each PUT as a new file), each retry will create another file with the same name, resulting in duplicate artifacts.

Confirmed Facts

• The <retryCount> and <backoff> elements only control how many times the HTTP client retries a failed PUT; they do not add any idempotency logic.
• Repository managers such as Nexus, Artifactory, and Archiva implement overwrite-on-PUT, making retries safe.
• Plain file-based or basic HTTP repositories that store each PUT as a new file are not idempotent; retries can produce duplicate entries.
• Maven’s wagon HTTP provider does not inspect repository semantics; the user must ensure safety via repository configuration or by disabling retries.

Steps to Configure Safely

1. Identify the repository type: Determine if it is a repository manager (Nexus, Artifactory, Archiva) or explicitly documented to support overwrite-on-PUT. If unsure, proceed to the verification step.
2. Verify PUT behavior (if needed):
   • Deploy a test artifact to the repository.
   • Interrupt the network mid-PUT (e.g., disconnect or cause a timeout).
   • Observe whether a second upload creates a duplicate file with the same name or simply replaces the existing one.
   If a duplicate appears, the repository is not idempotent.
3. Configure wagon settings (only if the repository is idempotent):

   <server>
       <id>your-repo-id</id>
       <configuration>
         <retryCount>3</retryCount>  
         <backoff>1000</backoff>   
       </configuration>
     </server>

4. Disable retries for non-idempotent targets: Set <retryCount>0</retryCount> (or omit the element) for those repositories to avoid duplicate uploads.

Missing Diagnostic Detail

To give a definitive recommendation, please confirm whether your target repository treats HTTP PUT as an idempotent operation (overwrites existing files) or as a create-only operation. This detail determines whether you can safely enable <retryCount> or must disable it.