[jira] [Created] (MAPREDUCE-7547) HsWebApp should bind App request-scoped instead of singleton

["Jose Luis López (Jira)" <ji...@apache.org>]

Jose Luis López created MAPREDUCE-7547:
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             Summary: HsWebApp should bind App request-scoped instead of singleton
                 Key: MAPREDUCE-7547
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-7547
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: webapps, jobhistoryserver
            Reporter: Jose Luis López


MAPREDUCE-7527 fixed the JobHistoryServer attempts page by binding {{App}} as a singleton in {{HsWebApp.setup()}}:

{code:java}
bind(App.class).in(Singleton.class);
{code}

{{App}} holds per-request mutable state: {{AppController.requireJob()}} / {{requireTask()}} (inherited by {{HsController}}) call {{app.setJob(...)}} / {{app.setTask(...)}}, and the rendered view reads them back via {{app.getJob()}} / {{app.getTask()}}. With a singleton, every request to the JHS shares one {{App}} instance, so concurrent requests can overwrite each other's job/task and a page can render data for a different job than the one requested.

The equivalent fix for the AM web UI, MAPREDUCE-7541 (https://github.com/apache/hadoop/pull/8652), was reviewed with this exact concern and uses request scope instead:

{code:java}
bind(App.class).in(RequestScoped.class);
{code}

The JHS is long-lived and serves all users, so it should use the same request-scoped binding.

*Proposed change*
* In {{HsWebApp.setup()}}, change {{Singleton.class}} to {{com.google.inject.servlet.RequestScoped.class}}.
* Add a regression test that starts the JHS web app and requests {{/jobhistory/attempts/<job_id>/m/SUCCESSFUL}}, asserting attempt rows are rendered (guards MAPREDUCE-7527), and ideally that two different jobs' pages each render their own job.




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