Automating the creation of a MongoDB ReplicaSet

I have revisited an old Github Gist of mine, adding some bash nicety to allow the user to specify the number of servers and the starting port range.

	#!/bin/bash
	#
	# Starts up a MongoDB replica set
	#
	# There is a lot of documentation about replica sets:
	#
	# http://docs.mongodb.org/manual/reference/replica-configuration/
	# http://docs.mongodb.org/manual/administration/replica-sets/
	#
	# To read data from a SECONDARY, when in the client, use:
	#
	# > rs.slaveOk()
	#
	# Created by M. Massenzio, 2012-05-10

	# Prints usage
	function usage {
	echo "Usage: `basename $0` replicaSetName [num] [port] [host]

	Creates a replica set of 'num' MongoDB servers, running on consecutive ports
	starting at 'port' on the same 'host' ('localhost' by default).

	By default, it will start 3 servers, on ports {27011, 27012, 27013}.

	Due to bash limited ability to parse command-line args, each argument MUST
	be present, if any of the subsequent ones need to be specified.

	The replicaSetName is required and can be used when connecting to
	the set, using a URI of the form:

	mongodb://host:27011,host:27012,host:27013?replicaSet='replicaSetName'
	"
	}

	# Creates a replica set member's record for the configuration
	#
	# Arguments:
	# $1 id
	# $2 host
	function create_record {
	echo "{ \"_id\": $1, \"host\": \"$2\"}"
	}

	# Initialize the replica set
	#
	# Arguments:
	# $1 primary mongod port (uses global: HOST)
	# $2 replica set configuration record
	function initialize_repset {
	if [[ -z "$2" ]]; then
	echo "No configuration record passed"
	exit 1
	fi
	local CFG_REC="$2"
	echo -e "rsconf = ${CFG_REC}\nrs.initiate(rsconf)" \| \
	mongo –port $1 –host ${HOST} > /dev/null
	}

	# Waits for the state of all mongo servers to get past the STARTUP phases
	#
	# Arguments:
	# $1 a port for the mongo client to connect to (default: 27011)
	# $2 the host to connect to (default: localhost)
	function wait_for_repset {
	local PORT=${1:-27011}
	local H=${2:-localhost}
	while true; do
	num=$(echo "rs.status()" \| mongo –port $PORT –host $H \| grep stateStr \| grep -v STARTUP \| wc -l)
	if [[ $(expr $num) == ${NUM_REPLICAS} ]]; then
	return
	fi
	sleep 1
	done
	}

	# Main body of script starts here
	# TODO: factor out sub-sections in their own functions

	if [[ -z "$1" ]]; then
	usage
	exit 1
	fi

	declare -r REPSET_NAME="$1"
	declare -r NUM_REPLICAS=${2:-3}
	declare -r STARTING_PORT=${3:-27011}
	declare -r HOST=${4:-localhost}

	echo "[INFO] Starting ${NUM_REPLICAS} MongoDB servers on ${HOST}, " \
	" using ports starting at ${STARTING_PORT};" \
	" the replica set will be named: ${REPSET_NAME}"
	read -p "Do you want to continue (y/N)? " resp
	if [[ $resp != 'y' ]]; then
	echo "Terminating."
	exit 1
	fi

	if [[ -z ${MONGO_BASE} ]]; then
	echo "[WARN] Please define \$MONGO_BASE to point to where you want data/logs to be created"
	MONGO_BASE=${HOME}/mongod_base
	read -p "Would you like to continue using the default (${MONGO_BASE})? " resp
	if [[ $resp != 'y' ]]; then
	echo "Terminating."
	exit 1
	fi
	fi
	echo "Using base directory for logs and data: ${MONGO_BASE}"
	declare -r LOGS_DIR="${MONGO_BASE}/logs"
	declare -r DATA_DIR="${MONGO_BASE}/data"

	mkdir -p ${LOGS_DIR}
	echo "Logs sent to ${LOGS_DIR}, data saved in ${DATA_DIR}"

	if [[ ! -d ${LOGS_DIR} \|\| ! -d ${DATA_DIR} ]]; then
	echo "[ERROR] Either logs or data directory could not be found/created; aborting."
	exit 1
	fi

	MEMBERS=""
	PORT=${STARTING_PORT}
	for ((i=1; i <= ${NUM_REPLICAS}; i++))
	do
	mkdir -p "${DATA_DIR}/${REPSET_NAME}_${i}"
	LOGPATH="${LOGS_DIR}/${REPSET_NAME}_${i}.log"
	DBPATH="${DATA_DIR}/${REPSET_NAME}_${i}"
	mongod –rest –replSet "${REPSET_NAME}" –logpath $LOGPATH \
	–dbpath $DBPATH –port ${PORT} –fork –vvvvv \
	–smallfiles –oplogSize 128 > /dev/null
	echo "[INFO] MongoDB server started on port $PORT"
	MEMBERS="$MEMBERS $(create_record $i ${HOST}:${PORT})"
	if [[ $i < ${NUM_REPLICAS} ]]; then
	MEMBERS="${MEMBERS},"
	fi
	((PORT++))
	done
	CONFIG="{ _id: \"${REPSET_NAME}\", members: [${MEMBERS}]}"
	echo "[INFO] Configuring replica set ${REPSET_NAME} and initializing"
	initialize_repset ${STARTING_PORT} "${CONFIG}"
	if [[ $? != 0 ]]; then
	echo "[ERROR] could not initialize the replica set [${REPSET_NAME}]"
	exit 1
	fi
	echo "[SUCCESS] Replica set ${REPSET_NAME} started and configured"
	echo "[INFO] Waiting for replica set to sync and elect primary…"
	wait_for_repset ${STARTING_PORT} ${HOST}
	echo "[SUCCESS] To connect to PRIMARY execute: mongo –port ${STARTING_PORT} –host ${HOST}"

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repset_mongo.sh
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This is really meant to be used solely for test / development purposes (really, what’s the point of having a replica set running off a single server in Production?).

Usage would be something like:

[~] $ repset-mongo.sh test-rs0 5 30100
[INFO] Starting 5 MongoDB servers on localhost, using ports starting at 30100;
the replica set will be named: test-rs0
Do you want to continue (y/N)? y
[WARN] Please define $MONGO_BASE to point to where you want data/logs to be created
Would you like to continue using the default (/Users/marco/mongod_base)? y
Using base directory for logs and data: /Users/marco/mongod_base
Logs sent to /Users/marco/mongod_base/logs, data saved in /Users/marco/mongod_base/data
[INFO] MongoDB server started on port 30100
[INFO] MongoDB server started on port 30101
[INFO] MongoDB server started on port 30102
[INFO] MongoDB server started on port 30103
[INFO] MongoDB server started on port 30104
[INFO] Configuring replica set test2 and initializing
[SUCCESS] Replica set test2 started and configured
[INFO] Waiting for replica set to sync and elect primary...
[SUCCESS] To connect to PRIMARY execute: mongo --port 30100 --host localhost

If you specify an environment variable $MONGO_BASE, data and logs will be placed there; otherwise, the script will by default use ${HOME}/mongo_base.

Again, use this just to do some quick tests in a dev environment.

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