100 lines
3.3 KiB
Bash
100 lines
3.3 KiB
Bash
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#!/usr/bin/env bash
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# A bash implementation of http://code.openark.org/blog/mysql/leader-election-using-mysql
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# Defaults
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quorum_alive_command='/bin/true'
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quorum_config='/etc/quorum.conf'
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quorum_db='quorum'
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quorum_db_command='/usr/bin/mysql'
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quorum_host='localhost'
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quorum_id=$(hostname -f)
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quorum_interval='20'
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quorum_notify_command='/usr/bin/echo alive status:${QUORUM_ALIVE_STATUS}, leader: ${QUORUM_LEADER}, my leader status: ${QUORUM_LEADER_STATUS}'
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quorum_password='quorum'
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quorum_table='service_election'
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quorum_user='quorum'
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# Override default config path from env
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if [[ "x${QUORUM_CONFIG}" != "x" ]]; then
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quorum_config="${QUORUM_CONFIG}"
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fi
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# Override default config with settings from config file
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if [[ -f "${quorum_config}" ]]; then
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. "${quorum_config}"
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fi
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# Override with env
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if [[ "x${QUORUM_ALIVE_COMMAND}" != "x" ]]; then
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quorum_alive_command=${QUORUM_ALIVE_COMMAND}
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fi
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if [[ "x${QUORUM_DB}" != "x" ]]; then
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quorum_db=${QUORUM_DB}
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fi
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if [[ "x${QUORUM_DB_COMMAND}" != "x" ]]; then
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quorum_db_command=${QUORUM_DB_COMMAND}
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fi
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if [[ "x${QUORUM_HOST}" != "x" ]]; then
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quorum_host=${QUORUM_HOST}
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fi
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if [[ "x${QUORUM_ID}" != "x" ]]; then
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quorum_id=${QUORUM_ID}
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fi
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if [[ "x${QUORUM_INTERVAL}" != "x" ]]; then
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quorum_interval=${QUORUM_INTERVAL}
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fi
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if [[ "x${QUORUM_NOTIFY_COMMAND}" != "x" ]]; then
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quorum_notify_command=${QUORUM_NOTIFY_COMMAND}
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fi
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if [[ "x${QUORUM_PASSWORD}" != "x" ]]; then
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quorum_password=${QUORUM_PASSWORD}
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fi
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if [[ "x${QUORUM_TABLE}" != "x" ]]; then
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quorum_table=${QUORUM_TABLE}
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fi
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if [[ "x${QUORUM_USER}" != "x" ]]; then
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quorum_user=${QUORUM_USER}
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fi
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# MySQL command
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quorum_db_command="${quorum_db_command} --database=${quorum_db} --user ${quorum_user} --password ${quorum_password}"
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# Queries
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create_table_query='CREATE TABLE ${quorum_table} (
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anchor tinyint(3) unsigned NOT NULL,
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service_id varchar(128) NOT NULL,
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last_seen_active timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
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PRIMARY KEY (anchor)
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) ENGINE=InnoDB'
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table_exists_query="SELECT *
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FROM information_schema.tables
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WHERE table_schema = '${quorum_db}'
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AND table_name = '${quorum_table}'
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LIMIT 1"
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election_query="insert ignore into ${quorum_table} ( anchor, service_id, last_seen_active ) values ( 1, '${quorum_id}', now() ) on duplicate key update service_id = if(last_seen_active < now() - interval ${quorum_interval} second, values(service_id), service_id), last_seen_active = if(service_id = values(service_id), values(last_seen_active), last_seen_active)"
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is_leader_query="select count(*) as is_leader from ${quorum_table} where anchor=1 and service_id='${quorum_id}'"
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who_is_leader_query="select max(service_id) as leader from ${quorum_table} where anchor=1"
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# Set up table if it does not exist
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${quorum_db_command} -e "${table_exists_query}" >/dev/null 2>&1
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if [[ ${?} -ne 0 ]]; then
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${quorum_db_command} -e "${create_table_query}" >/dev/null 2>&1
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fi
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# Run the algorithm
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${quorum_alive_command} >/dev/null 2>&1
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alive_status=${?}
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if [[ ${alive_status} -eq 0 ]]; then
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${quorum_db_command} -e "${election_query}" >/dev/null 2>&1
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fi
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leader_status=$(${quorum_db_command} -e "${is_leader_query}")
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leader=$(${quorum_db_command} -e "${who_is_leader_query}")
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QUORUM_ALIVE_STATUS=${alive_status} QUORUM_LEADER=${leader} QUORUM_LEADER_STATUS=${leader_status} eval ${quorum_notify_command}
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exit ${alive_status}
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