ruby-2.0.0-p195 + fluentd 0.10.35の組み合わせでログの重複現象が確認できた fluent.conf:

gistfile1.apacheconf

## built-in TCP input
## $ echo <json> | fluent-cat <tag>
<source>
  type forward
</source>

# HTTP input
# http://localhost:8888/<tag>?json=<json>
<source>
  type http
  port 8888
</source>

<source>
  type tail
  format ltsv
  time_key time
  path /var/log/apache2/project/project.acc.log
  pos_file /var/log/fluent/log.pos
  tag apache.access
</source>

<source>
  type tail
  format json
  path /opt/xxx/fs/project/contents/app/tmp/logs/json.log
  pos_file /var/log/fluent/app-log.pos
  tag app.log
</source>

# Listen DRb for debug
<source>
  type debug_agent
  port 24230
</source>

<match apache.access>
    type copy
    <store>
    type file
    path /opt/xxx/fs/fluent/project/apache.local.acc
    </store>
    <store>
    type forward
    buffer_chunk_limit 8m
    buffer_queue_limit 128
    retry_limit 16
    flush_interval 1s
    flush_at_shutdown
    buffer_type file
    buffer_path /var/log/fluent/buffer/project.acc
    <server>
      name lg001-01
      host lg001
      port 24224
      weight 50
    </server>
#    <server>
#      name lg001-02
#      host lg001
#      port 24225
#      weight 60
#    </server>
#    <server>
#      name lg001-03
#      host lg001
#      port 24226
#      weight 60
#    </server>
#    <server>
#      name lg001-04
#      host lg001
#      port 24227
#      weight 60
#    </server>
    <server>
      name lg002-01
      host lg002
      port 24224
      weight 50
    </server>
#    <server>
#      name lg002-02
#      host lg002
#      port 24225
#      weight 60
#    </server>
#    <server>
#      name lg002-03
#      host lg002
#      port 24226
#      weight 60
#    </server>
#    <server>
#      name lg002-04
#      host lg002
#      port 24227
#      weight 60
#    </server>
    <secondary>
      type file
      path /var/log/fluent/project/forward-failed/project.acc
    </secondary>
    </store>
</match>

<match app.log>
  type forward
    buffer_chunk_limit 8m
    buffer_queue_limit 128
    retry_limit 16
    flush_interval 1s
    flush_at_shutdown
    buffer_type file
    buffer_path /var/log/fluent/buffer/app.log
    <server>
      name lg001-01
      host lg001
      port 24224
      weight 50
    </server>
#    <server>
#      name lg001-02
#      host lg001
#      port 24225
#    </server>
#    <server>
#      name lg001-03
#      host lg001
#      port 24226
#      weight 10
#    </server>
    <server>
      name lg002-01
      host lg002
      port 24224
      weight 50
    </server>
#    <server>
#      name lg002-02
#      host lg002
#      port 24225
#    </server>
#    <server>
#      name lg002-03
#      host lg002
#      port 24226
#      weight 10
#    </server>
    <secondary>
      type file
      path /var/log/fluent/project/forward-failed/app.log
    </secondary>
</match>

## match tag=debug.** and dump to console
<match debug.**>
  type stdout
</match>

## match not matched logs and write to file
<match **>
  type file
  path /var/log/fluent/else/else
</match>

/opt/xxx/fs/fluent/project/apache.local.acc.YYYYMMDD_#.log 個々では重複していないが、ruby 2.0.0 p195 + fluentd 0.10.35使用時に cat *.log | sort | uniq -d | wc -l で重複していることが確認できた。気になっている点は

• apache 2.4の rotatelog -L オプションで最新のログへのハードリンクを生成させてそれを監視させている
• rotatelogは 1日に一度のrotateなのだが fluentdのログで
  2013-07-29 19:07:10 +0900 [info]: detected rotation of /var/log/apache2/project/project.acc.log; waiting 5 seconds
  2013-07-29 19:07:10 +0900 [info]: detected rotation of /var/log/apache2/project/project.acc.log
  2013-07-29 19:07:10 +0900 [info]: following tail of /var/log/apache2/project/project.acc.log
  が不定期に発生している。そのタイミングでハッシュ付きのファイル名からログが生成されている