Hi Evans! What is the best medium to use for the documentation/comments ? A shared gdoc or something similar?
Luca On Thu, Jul 16, 2020 at 5:11 PM Evans Ye <[email protected]> wrote: > > One thing I think would be great to have is a doc version of the steps for > upgrade and rollback. The benefits: > 1. Anything unexpected happened during automation, you do have folks can > quickly understand what's going on and get into the investigation. > 2. Share the doc with us to help the others OSS users for doing the > migration. For the env specific things I think that's fine. We can left > comment on it. At least all the other users can get a high level view of a > proven solution. And then they can go and find out the rest of the pieces by > themselves. > > For automations, I suggest to split up the automation into several stages, > and apply some validation steps(manually is ok) before kicking of the next > stage. > > Best, > Evans > > > > > Luca Toscano <[email protected]> 於 2020年7月15日 週三 下午9:07寫道： >> >> Hi everybody, >> >> I didn't get the time to work on this until recently, but I finally >> managed to have a reliable procedure to upgrade from CDH to Bigtop 1.4 >> and rollback if needed. The assumptions are: >> >> 1) It is ok to have (limited) cluster downtime. >> 2) Rolling upgrade is not needed. >> 3) QJM is used. >> >> The procedure is listed in these two scripts: >> >> https://github.com/wikimedia/operations-cookbooks/blob/master/cookbooks/sre/hadoop/stop-cluster.py >> https://github.com/wikimedia/operations-cookbooks/blob/master/cookbooks/sre/hadoop/change-distro-from-cdh.py >> >> The code is highly dependent on my working environment, but it should >> be clear to follow when writing a tutorial about how to migrate from >> CDH to Bigtop. All the suggestions given by this mailing list were >> really useful to reach a solution! >> >> My next steps will be: >> >> 1) Keep testing Bigtop 1.4 (finalize HDFS upgrade, run more hadoop >> jobs, test Hive 2, etc..). >> 2) Upgrade the production Hadoop cluster to Bigtop 1.4 on Debian 9 >> (HDFS 2.6.0-cdh -> 2.8.5). >> 3) Upgrade to Bigtop 1.5 on Debian 9 (HDFS 2.8.5 -> 2.10). >> 4) Upgrade to Debian 10. >> >> With automation it shouldn't be very difficult, I'll report progress once >> made. >> >> Thanks a lot! >> >> Luca >> >> On Mon, Apr 13, 2020 at 9:25 AM Luca Toscano <[email protected]> wrote: >> > >> > Hi Evans, >> > >> > thanks a lot for the feedback, it was exactly what I needed. The >> > simpler the better is definitely a good advice in this use case, I'll >> > try this week another rollout/rollback and report back :) >> > >> > Luca >> > >> > On Thu, Apr 9, 2020 at 8:09 PM Evans Ye <[email protected]> wrote: >> > > >> > > Hi Luca, >> > > >> > > Thanks for reporting back and let us know how it goes. >> > > I don't have the exactly HDFS with QJM HA upgrade experience. The >> > > experience I had was 0.20 non-HA upgrade to 2.0 non-HA and then enable >> > > QJM HA, which was back in 2014. >> > > >> > > Regarding to rollback, I think you're right: >> > > >> > > it is possible to rollback to HDFS’ state before the upgrade in case of >> > > unexpected problems. >> > > >> > > My previous experience is the same that the rollback is merely a >> > > snapshot before the upgrade. If you've gone far, then rollback cost more >> > > data lost... Our runbook is if our sanity check failed during upgrade >> > > downtime, we perform the rollback immediately. >> > > >> > > Regarding to that FSImage hole issue, I've experienced it as well. >> > > I managed to fix it by manually edit the FSImage with offline image >> > > viewer[1] and delete that missing editLog in FSImage. That actually >> > > brought my cluster back with a little number of missing blocks. >> > > >> > > Our experience says that the more the steps, the more the chance you >> > > failed the upgrade. We did good on dozen times of testing, DEV cluster, >> > > STAGING cluster, but still got missing blocks when upgrading >> > > Production... >> > > >> > > The suggestion is to get your production in good shape first(the less >> > > decommissioned, offline DNs, disk failures, the better). >> > > Also, maybe you can switch to non-HA mode and do the upgrade to simplify >> > > the things? >> > > >> > > Not many helps but please let us know if any progress. >> > > Last one, have you reached out to Hadoop community? the authors should >> > > know the most :) >> > > >> > > - Evans >> > > >> > > [1] >> > > https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsImageViewer.html >> > > >> > > Luca Toscano <[email protected]> 於 2020年4月8日 週三 21:03 寫道： >> > >> >> > >> Hi everybody, >> > >> >> > >> most of the bugs/issues/etc.. that I found while upgrading from CDH 5 >> > >> to BigTop 1.4 are fixed, I am now testing (as suggested also in here) >> > >> upgrade/rollback procedures for HDFS (all written in >> > >> https://phabricator.wikimedia.org/T244499, will add documentation >> > >> about this at the end I promise). >> > >> >> > >> I initially followed [1][2] in my Test cluster, choosing the Rolling >> > >> upgrade, but when I tried to rollback (after days since the initial >> > >> upgrade) I ended up in an inconsistent state and I wasn't able to >> > >> recover the previous HDFS state. I didn't save the exact error >> > >> messages but the situation was more or less the following: >> > >> >> > >> FS-Image-rollback (created at the time of the upgrade) - up to >> > >> transaction X >> > >> FS-Image-current - up to transaction Y, with Y = X + 10000 (number >> > >> totally made up for the example) >> > >> QJM cluster: first available transaction Z = X + 10000 + 1 >> > >> >> > >> When I tried to rolling rollback, the Namenode complained about a hole >> > >> in the transaction log, namely at X + 1, so it refused to start. I >> > >> tried to force a regular rollback, but the Namenode refused again >> > >> saying that there was no available FS Image to roll back to. I checked >> > >> in the Hadoop code and indeed the Namenode saves the fs image with >> > >> different naming/path in case of a rolling upgrade or a regular >> > >> upgrade. Both cases make sense, especially the first one since there >> > >> was indeed a hole between the last transaction of the >> > >> FS-Image-rollback and the first available transaction to reply on the >> > >> QJM cluster. I chose the rolling upgrade initially since it was >> > >> appealing: it promises to bring back the Namenodes to their previous >> > >> versions, but keeping the data modified between upgrade and rollback. >> > >> >> > >> I then found [3], in which it is said that with QJM everything is more >> > >> complicated, and a regular rollback is the only option available. What >> > >> I think this mean is that due to the Edit log spread among multiple >> > >> nodes, a rollback that keeps data between upgrade and rollback is not >> > >> available, so worst case scenario the data modified during that >> > >> timeframe is lost. Not a big deal in my case, but I want to triple >> > >> check with you if this is the correct interpretation or if there is >> > >> another tutorial/guide/etc.. that I haven't read with a different >> > >> procedure :) >> > >> >> > >> Is my interpretation correct? If not, is there anybody with experience >> > >> in HDFS upgrades that could shed some light on the subject? >> > >> >> > >> Thanks in advance! >> > >> >> > >> Luca >> > >> >> > >> >> > >> >> > >> [1] >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsUserGuide.html#Upgrade_and_Rollback >> > >> [2] >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HdfsRollingUpgrade.html >> > >> [3] >> > >> https://hadoop.apache.org/docs/r2.8.5/hadoop-project-dist/hadoop-hdfs/HDFSHighAvailabilityWithQJM.html#HDFS_UpgradeFinalizationRollback_with_HA_Enabled
