Hi Luca, I read through the doc briefly. I think the doc works very well as a blogpost of a successful story for Wikimedia migrating from CDH to Bigtop. However, the current writing doesn't seem to be easily consumable for users' who are just looking into the solutions/steps for doing similar migrations. May I know what title you would prefer if we put the doc in Bigtop's wiki?
What I was thinking is the cookbook for migration. But we can discuss this. IMHO a Success at Apache[1] blogpost is also possible. But I need to figure out who to talk to. Let me know what you think. [1] https://blogs.apache.org/foundation/category/SuccessAtApache Evans Evans Ye <evan...@apache.org> 於 2020年8月30日 週日 上午3:18寫道： > Hi Luca, > > I'm on vacation hence do not have time for review right now. I'll get back > to you next week. > > The doc is definitely valuable. Once you have your production migrated > successfully. We can prove to the other users that this is a battle proven > solution. Even more, we can give a talk at ApacheCon or somewhere else to > further amplify the impact of the work. This is definitely an open source > winning case so I think it deserve a talk. > > Evans > > > Luca Toscano <toscano.l...@gmail.com> 於 2020年8月27日 週四 下午9:11寫道： > >> Hi Evans, >> >> it took a while I know but I have the first version of the gdoc for the >> upgrade: >> >> >> https://docs.google.com/document/d/1fI1mvbR1mFLV6ohU5cIEnU5hFvEE7EWnKYWOkF55jtE/edit?usp=sharing >> >> I tried to list all the steps involved in migrating from CDH 5 to >> Bigtop 1.4, anybody interested should be able to comment. The idea >> that I have is to discuss this for a few days and then possibly make >> it permanent somewhere in the Bigtop wiki? (of course if the document >> will be considered useful for others etc..) >> >> During these days I tested the procedure multiple times, and I have >> also tested the HDFS finalize step, everything works as expected. I >> hope to be able to move to Bigtop during the next couple of months. >> >> Luca >> >> On Tue, Jul 21, 2020 at 4:04 PM Evans Ye <evan...@apache.org> wrote: >> > >> > Yes. I think a shared gdoc is prefered, and you can open up a JIRA >> ticket to track it. >> > >> > Luca Toscano <toscano.l...@gmail.com> 於 2020年7月20日 週一 21:10 寫道： >> >> >> >> 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 <evan...@apache.org> 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 <toscano.l...@gmail.com> 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 < >> toscano.l...@gmail.com> 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 <evan...@apache.org> >> 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 <toscano.l...@gmail.com> 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 >> >
