how to check if mongodb is up and ready to accept connections from bash script? - bash

Question

I have a bash shell script which does a bunch of stuff before trying to mongorestore.
I want to make sure that not only MongoDB is up, but it is also ready to accept connections before i try restore.
Right now, what I am seeing is, mongo process is up but it take 45+ seconds to do the initial setup (setting up journal files etc) before it is ready to accept connections. Ideally I want to keep testing the connection in a loop and only when I am able to connect, I want to run mongorestore.
Can someone show me how to do this in Bash or point me in the right direction?

Answer 1

To test the connection in a loop like you suggest,
until nc -z localhost 27017
do
sleep 1
done

Answer 2

A solution using MongoDB Tools. Useful in a docker container or something similiar where you do not want to install nc.
until mongo --eval "print(\"waited for connection\")"
do
sleep 60
done
Based on that other guy's answer.

Answer 3

I recently had the same problem. I decided to configure mongod to log all it's output to a logfile and then wait in a loop checking the logfile until we see some output that suggests mongod is ready.
This is an example logfile output line we need to wait for:
Tue Dec 3 14:25:28.217 [initandlisten] waiting for connections on port 27017
This is the bash script I came up with:
#!/bin/bash
# Initialize a mongo data folder and logfile
mkdir -p /data/db
touch /var/log/mongodb.log
# Start mongodb with logging
# --logpath Without this mongod will output all log information to the standard output.
# --logappend Ensure mongod appends new entries to the end of the logfile. We create it first so that the below tail always finds something
/usr/bin/mongod --quiet --logpath /var/log/mongodb.log --logappend &
# Wait until mongo logs that it's ready (or timeout after 60s)
COUNTER=0
grep -q 'waiting for connections on port' /var/log/mongodb.log
while [[ $? -ne 0 && $COUNTER -lt 60 ]] ; do
sleep 2
let COUNTER+=2
echo "Waiting for mongo to initialize... ($COUNTER seconds so far)"
grep -q 'waiting for connections on port' /var/log/mongodb.log
done
# Now we know mongo is ready and can continue with other commands
...
Notice the script will not wait forever, it will timeout after 60s - you may or may not want that depending on your use case.

Answer 4

I needed Mongo running in Docker to initialize before creating a user. I combined the answers of Tom and Björn. This is the script I am using:
#!/bin/bash
# Wait until Mongo is ready to accept connections, exit if this does not happen within 30 seconds
COUNTER=0
until mongo --host ${MONGO_HOST} --eval "printjson(db.serverStatus())"
do
sleep 1
COUNTER=$((COUNTER+1))
if [[ ${COUNTER} -eq 30 ]]; then
echo "MongoDB did not initialize within 30 seconds, exiting"
exit 2
fi
echo "Waiting for MongoDB to initialize... ${COUNTER}/30"
done
# Connect to the MongoDB and execute the create users script
mongo ${FWRD_API_DB} /root/create-user.js --host ${MONGO_HOST} -u ${MONGO_ROOT_USER} -p ${MONGO_ROOT_PASSWORD} --authenticationDatabase admin

Answer 5

While Tom's answer will work quite well in most situations, it can fail if you are running your script with the -e flag. I mean you run your script with set -e at the very top. Why? Because Tom's answer relies on the exit status of the previous command, in this case grep -q which will fail if it does not find the required string, and therefore the entire script will fail. The -e flag documentation gives a clue on how to avoid this problem:
The shell does not exit if the command that fails is part of the
command list immediately following a while or until keyword, part of
the test in an if statement, part of any command executed in a && or
|| list except the command following the final && or ||, any command
in a pipeline but the last, or if the command’s return status is being
inverted with !.
So, one solution is to make the grep command part of the while condition. However, since he is running mongodb with the --logappend option the search string could appear as a result of a previous run. I combined that other guy answer with Tom's answer and it works really well:
# Wait until mongo logs that it's ready (or timeout after 60s)
COUNTER=0
while !(nc -z localhost 27017) && [[ $COUNTER -lt 60 ]] ; do
sleep 2
let COUNTER+=2
echo "Waiting for mongo to initialize... ($COUNTER seconds so far)"
done
I find that using tomcat is the best solution because it actually tests if there is something listening.

Answer 6

Possible Docker solution:
Given the docker_id for me it works reading the docker logs like:
until [ $(docker logs --tail all $docker_id | grep "waiting for connections on port" | wc -l) -gt 0 ]; do
printf '.'
sleep 1
done
then continue with any mongo-dependent task.

Answer 7

This approach is using in bitnami mongodb helm chart, but requires installed mongodb shell client:
mongosh --host {your_mongo_host} --port {your_mongo_port} --eval "db.adminCommand('ping')"