"We can't communicate with your server" starting attachment-only migration
Platform notice: Server and Data Center only. This article only applies to Atlassian products on the Server and Data Center platforms.
Support for Server* products ended on February 15th 2024. If you are running a Server product, you can visit the Atlassian Server end of support announcement to review your migration options.
*Except Fisheye and Crucible
Summary
Learn what to do when your attachment-only migration throws "We can't communicate with your server" with the Confluence Cloud Migration Assistant (CCMA).
Overview
Right after initiating an attachment-only migration with the CCMA, a dialog with this error message appears in the interface.
The error message comes along the below signature in the application log file atlassian-confluence.log:
ERROR [agent.service.impl.DefaultPlanService] startPlan Fail to start the plan: <plan-name>
-- referer: <confluence-base-url> | url: /rest/migration/latest/plan/<plan-id>/start | traceId: YYYYY | userName: XXXXXX
java.lang.IllegalArgumentException: A plan must have at least one task.
at com.atlassian.migration.agent.service.execution.PlanExecutionService.lambda$runPlan$1(PlanExecutionService.java:247)
at com.atlassian.migration.agent.store.jpa.impl.DefaultPluginTransactionTemplate.on(DefaultPluginTransactionTemplate.java:36)
at com.atlassian.migration.agent.store.tx.PluginTransactionTemplate.write(PluginTransactionTemplate.java:24)
...This happens because the attachment-only migration option was selected, but no spaces were selected with it.
It's necessary to select at least one space when doing an attachment-only migration.
Solution
Try the attachment-only migration selecting the spaces for which you want the attachments to be uploaded to Confluence Cloud.
The selected spaces data won't be migrated, only the spaces attachments.