From b90350247e8429c147c4a6a984bc9c6ba9c57785 Mon Sep 17 00:00:00 2001
From: jlecour <jlecour+gitit@evolix.fr>
Date: Thu, 20 Oct 2022 17:03:24 +0200
Subject: [PATCH] =?UTF-8?q?Guide=20pour=20faire=20du=20master/replica=20su?=
 =?UTF-8?q?rveill=C3=A9=20par=20HAProxy?=
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---
 HowtoRedis.md | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 166 insertions(+)

diff --git a/HowtoRedis.md b/HowtoRedis.md
index cce9ac79..f81c9a85 100644
--- a/HowtoRedis.md
+++ b/HowtoRedis.md
@@ -423,6 +423,172 @@ Sentinel doit pouvoir ecrire dans son fichier de configuration :
 chown redis: /etc/redis/sentinel.conf
 ~~~
 
+## Load-balancing avec HAProxy
+
+Il est possible d'avoir un master et plusieurs replica derrière un proxy/load-balancer HAProxy (sur `172.19.3.100` dans l'exemple).
+
+~~~.haproxy
+frontend fe_redis
+    mode tcp
+    option tcplog
+
+    bind 127.0.0.1:6379
+
+    default_backend be_redis
+
+backend be_redis
+    mode tcp
+    balance first
+
+    default-server maxconn 1024 check agent-check agent-port 16379 agent-inter 1s
+
+    server srv1 172.20.3.200:6379
+    server srv2 172.20.3.201:6379
+~~~
+
+Sur les serveurs avec Redis (`172.19.3.200` et `172.19.3.201` dans notre exemple), il faut installer le paquet `xinetd` puis créer une configuration `/etc/xinetd.d/haproxy-agent-redis-role` :
+
+~~~
+service haproxy-agent-redis-role
+{
+        socket_type     = stream
+        bind            = 172.19.3.200
+        port            = 16379
+        protocol        = tcp
+        wait            = no
+        type            = UNLISTED
+        user            = root
+        server          = /usr/share/scripts/haproxy-agent-redis-role.sh
+        log_on_failure  += USERID
+        disable         = no
+        only_from       = 172.19.3.100
+}
+~~~
+
+On active ce service dans `/etc/services` :
+
+~~~
+haproxy-agent-redis-role 16379/tcp
+~~~
+
+Puis on redémarre `xinetd` : `systemctl restart xinetd`
+
+Enfin, on installe le script qui sert d'agent `/usr/share/scripts/haproxy-agent-redis-role.sh` :
+
+~~~.bash
+#!/bin/sh
+
+set -u
+
+config_var() {
+    variable=$1
+    file=$2
+    test -f "${file}" && grep -E "^${variable}\s+.+$" "${file}" | awk '{ print $2 }' | sed -e "s/^[\"']//" -e "s/[\"']$//"
+}
+get_role() {
+    host=$(config_var "bind" "${conf_file}")
+    port=$(config_var "port" "${conf_file}")
+    pass=$(config_var "requirepass" "${conf_file}")
+
+    if [ -n "${pass}" ]; then
+        export REDISCLI_AUTH="${pass}"
+    fi
+
+    cmd="${redis_cli_bin} -h ${host} -p ${port} INFO REPLICATION"
+    ${cmd} 2>/dev/null | grep -Eo "role:\w+" | cut -d ':' -f2
+}
+get_status() {
+    systemctl is-active "${1}"
+}
+
+redis_cli_bin=$(command -v redis-cli)
+if [ -z "${redis_cli_bin}" ]; then
+    printf "%s\n" "down # missing redis"
+    exit 1
+fi
+if [ $# -lt 1 ]; then
+    service="redis-server.service"
+    conf_file="/etc/redis/redis.conf"
+else
+    service="redis-server@${1}.service"
+    conf_file="/etc/redis-${1}/redis.conf"
+fi
+if [ ! -r "${conf_file}" ]; then
+    printf "%s\n" "down # missing config"
+    exit 3
+fi
+
+status=$(get_status "${service}")
+
+case "${status}" in
+    active)
+        printf "%s " "up"
+        ;;
+    inactive)
+        printf "%s\n" "stopped # systemd:${status}"
+        exit 1
+        ;;
+    failed)
+        printf "%s\n" "fail # systemd:${status}"
+        exit 1
+        ;;
+    *)
+        printf "%s\n" "down # systemd:${status}"
+        exit 1
+        ;;
+esac
+
+role=$(get_role "${conf_file}")
+
+case "${role}" in
+    master)
+        printf "%s" "ready # role:master"
+        ;;
+    slave)
+        printf "%s" "maint # role:slave"
+        ;;
+    *)
+        printf "%s" "maint # role:unknown"
+        ;;
+esac
+printf "\n"
+
+exit 0
+~~~
+
+### Redis multi-instances
+
+Ce script est compatible avec la présence de multiples instances de Redis.
+
+Si on l'exécute avec un argument `foo` il cherchera une configuration `/etc/redis-foo/redis.conf` et un service systemd `redis-server@foo`.
+
+Il faudra alors déclarer autant de services xinetd que d'instances à surveiller :
+
+~~~
+haproxy-agent-redis-role-foo 16380/tcp
+haproxy-agent-redis-role-bar 16381/tcp
+~~~
+
+Et enfin, modifier les services pour ajouter le paramètre `server_args` :
+
+~~~
+service haproxy-agent-redis-role-foo
+{
+        socket_type     = stream
+        bind            = 172.19.3.200
+        port            = 16380
+        protocol        = tcp
+        wait            = no
+        type            = UNLISTED
+        user            = root
+        server          = /usr/share/scripts/haproxy-agent-redis-role.sh
+        server_args     = foo
+        log_on_failure  += USERID
+        disable         = no
+        only_from       = 172.19.3.100
+}
+~~~
+
 
 ## Benchmarks