Automated Backups in a replSet?

[Floppy Disk]

I have a replSet cluster running x2 MongoDB servers and an arbiter on a production Linux (CentOS 7.2) servers. I need to configure automated backups of the replSet but obviously I would need some kind of logic inside my script to detect rs.isMaster() & then perform a dump as follows:

mongodump -h 127.0.0.1 -d mydb -u carlos -p -o /var/lib/mongodb/backups

Thanks for any clarification or help in getting a basic working script for backing up my MongoDB / Linux deployment. I checked Google and didn't really find anything that was just basic guides randomly written years ago that don't work with a replSet.

Thanks!

-Carlos 

[davidmo]

hey carlos. i have a bash script on RHEL 6 and in the script this is how i check:

#
#   check if primary
#
PRIMARY=`/usr/bin/mongo ${SERVERNAME}:${PORT} --quiet ${SCRIPTDIR}/isMaster.js`;
#
#
# Check if any errors
#
if [ "$?" -ne "0" ]; then
    echo "Error running isMaster.js for $SERVERNAME" > ${LOGDIR}/dumplog.${DATE_NOW}
    cat ${LOGDIR}/dumplog.${DATE_NOW}  | mailx -s "ERROR mongodump output from $SERVERNAME" $EMAILIST
    exit 1
  fi
#
#
if [ "$PRIMARY" != "false" ]; then
    echo "No mongodump for ${SERVERNAME} - not the secondary" > ${LOGDIR}/dumplog.${DATE_NOW}
    cat ${LOGDIR}/dumplog.${DATE_NOW} | mailx -s "mongodump output from ${SERVERNAME}" $EMAILIST
    exit 2
fi
#

i only dump from a secondary.

[Floppy Disk]

Thanks David. I am a bit confused because you're setting a variable for 'PRIMARY' but I don't understand:
...${SCRIPTDIR}/isMaster.js`;

What is 'isMaster.js'? I am creating this backup script to backup the db inside /usr/local/sbin. Where do I need to have this isMaster.js script and what does that look like? I am fairly confused here so I apologize. 

I was going to have crontab just call the backup script /usr/local/sbin/mongodb-backup.sh:

#!/bin/sh

## Set variables

SCRIPTDIR='/usr/local/sbin/mongodb-backup.sh'

MONGOBIN='/usr/bin/'

SERVERNAME='mongo1.domain.tld'

LOGDIR='/var/log/mongodb/'

DATENOW='date +%Y%m%d%H%M%S'

## Check if the primary in cluster

PRIMARY='MONGO_BIN/mongo $SERVERNAME:27017 --quiet $SCRIPTDIR/isMaster.js';

# Check if any errors

if [ "$?" -ne "0" ]; then

    echo "Error running isMaster.js for $SERVERNAME" > $LOGDIR/mongodb-backup.$DATE_NOW

#   cat $LOGDIR/mongodb-backup.$DATE_NOW  | mailx -s "ERROR mongodump output from $SERVERNAME" $EMAILIST

    exit 1

fi

if [ "$PRIMARY" != "false" ]; then

    echo "No mongodump for $SERVERNAME - not the secondary" > $LOGDIR/dumplog.$DATE_NOW

#   cat $LOGDIR/mongodb-backup.$DATE_NOW | mailx -s "mongodump output from ${SERVERNAME}" $EMAILIST

    exit 2

fi

#

Where are you performing the dump? I see the shell script performing the check which I'm confused about above but also can you share the code for performing the dump as well?

[davidmo]

carlos, you asked about determining if a server is a PRIMARY or not.

i sent you the piece of my script that does that. PRIMARY is a variable that receives the ouput of executing isMaster.js

isMaster.js is a file that contains this:  printjson(db.isMaster().ismaster);

the dump is performed after the script determines that the server is not the PRIMARY using mongodump,  which is heavily documented.

On Tuesday, August 23, 2016 at 9:43:28 AM UTC-4, Floppy Disk wrote:

[boncalo mihai]

Hi Carlos,

It's simple to check if server is primary with  mongo --eval "printjson(db.isMaster())" and awk but for production environement rsync is recommended.

[davidmo]

carlos,

--eval is deprecated so using it is not a good idea.

On Tuesday, August 23, 2016 at 9:43:28 AM UTC-4, Floppy Disk wrote:

[Kevin Adistambha]

Hi Carlos,

I have a replSet cluster running x2 MongoDB servers and an arbiter on a production Linux (CentOS 7.2) servers. I need to configure automated backups of the replSet but obviously I would need some kind of logic inside my script to detect rs.isMaster() & then perform a dump as follows:

Do I understand correctly that you want to perform mongodump on a Secondary?

In MongoDB 3.0 and earlier, mongodump will always perform the dump from Secondaries if connected to a replica set.

This was changed in MongoDB 3.2, where mongodump defaults to Primary instead. In MongoDB 3.2, you can set the --readPreference setting to dump from Secondaries if you wish, giving you more flexibility. For example (if you are using MongoDB 3.2):

mongodump -h 127.0.0.1 -d mydb -u carlos -p -o /var/lib/mongodb/backups --readPreference=secondary

Please see mongodump read preference page for more details.

Also, please note that dumping from Secondaries is not recommended for a sharded cluster deployment. This is because Secondaries are eventually consistent with the Primary, and in a sharded cluster this could result in an inconsistent backup state.

Best regards,
Kevin

​

[boncalo mihai]

Hi Carlos,

it's true that --eval is deprecated but can still be found in mongo man page in 3.2 

The other way is to use a command like mongo --shell 'test.js'

where test.js contains 

printjson(db.isMaster())

printjson(quit())

and then get your info again with awk/cut or any other method you are familiar with.But still, I recommend full backup with rsync for primary

Michael.

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