Category: General

How to failover from Master to Replication node and visa versa

Pi6 192.168.2.106 (MASTER)

Pi7 192.168.2.107 (REPLICATION)

Make Replication node master

# Goto pi7

su postgres

/usr/lib/postgresql/13/bin/pg_ctl -D /data02/data promote
Restore old master

# Goto to pi6

sudo cp /data02/data/*.conf ../.

/usr/lib/postgresql/13/bin/pg_ctl -D /data02/data stop

rm -rf /data02/data/*

/usr/lib/postgresql/13/bin/pg_basebackup --pgdata=/data02/data --format=p --write-recovery-conf --checkpoint=fast --label=mffb --progress --host=pi7 --port=5432 --username=plaatsoft

rm /data02/data/standby.signal

/usr/lib/postgresql/13/bin/pg_ctl -D /data02/data start

psql -c "select * from pg_create_physical_replication_slot('standby1_slot');"
# Goto to pi7

sudo cp /data02/data/*.conf ../.

/usr/lib/postgresql/13/bin/pg_ctl -D /data02/data stop

rm -rf /data02/data/*

/usr/lib/postgresql/13/bin/pg_basebackup --pgdata=/data02/data --format=p --write-recovery-conf --checkpoint=fast --label=mffb --progress --host=pi6 --port=5432 --username=plaatsoft

/usr/lib/postgresql/13/bin/pg_ctl -D /data02/data start
Check replication
CHECK MASTER NODE

postgres=# \x

postgres=# SELECT * FROM pg_stat_replication;
postgres=# select pg_is_in_recovery();

pg_is_in_recovery

-------------------

f

(1 row)
CHECK REPLICATION NODE

postgres=# \x

postgres=# SELECT * FROM pg_stat_wal_receiver;
postgres=# select pg_is_in_recovery();

pg_is_in_recovery

-------------------

t

(1 row)
	

Execute on each Postgresql node the following actions

# Create check script
sudo vi /usr/lib/postgresql/13/bin/pgsqlchk

#!/bin/bash
# This script checks if a postgres server is healthy running on localhost. It will return:
# "HTTP/1.x 200 OK\r" (if postgres is running smoothly)
# - OR -
# "HTTP/1.x 500 Internal Server Error\r" (else)
# The purpose of this script is make haproxy capable of monitoring postgres properly
# It is recommended that a low-privileged postgres user is created to be used by this script.
# For eg. create user healthchkusr login password 'hc321';

PGBIN=/usr/pgsql-10/bin
PGSQL_HOST="localhost"
PGSQL_PORT="5432"
PGSQL_DATABASE="postgres"
PGSQL_USERNAME="postgres"
export PGPASSWORD="passwd"
TMP_FILE="/tmp/pgsqlchk.out"
ERR_FILE="/tmp/pgsqlchk.err"

# We perform a simple query that should return a few results

VALUE=`/usr/lib/postgresql/13/bin/psql -t -h localhost -U postgres -p 5432 -c "select pg_is_in_recovery()" 2> /dev/null`
# Check the output. If it is not empty then everything is fine and we return something. Else, we just do not return anything.

if [ $VALUE == "t" ]
then
/bin/echo -e "HTTP/1.1 206 OK\r\n"
/bin/echo -e "Content-Type: Content-Type: text/plain\r\n"
/bin/echo -e "\r\n"
/bin/echo "Standby"
/bin/echo -e "\r\n"
elif [ $VALUE == "f" ]
then
/bin/echo -e "HTTP/1.1 200 OK\r\n"
/bin/echo -e "Content-Type: Content-Type: text/plain\r\n"
/bin/echo -e "\r\n"
/bin/echo "Primary"
/bin/echo -e "\r\n"
else
/bin/echo -e "HTTP/1.1 503 Service Unavailable\r\n"
/bin/echo -e "Content-Type: Content-Type: text/plain\r\n"
/bin/echo -e "\r\n"
/bin/echo "DB Down"
/bin/echo -e "\r\n"
fi

# Make script executable
sudo chmod a+x /usr/lib/postgresql/13/bin/pgsqlchk

# install xinetd and telnet
sudo apt-get install xinetd telnet -y

# Create xinitd file
sudo vi /etc/xinetd.d/pgsqlchk

service pgsqlchk
{
flags = REUSE
socket_type = stream
port = 23267
wait = no
user = nobody
server = /usr/lib/postgresql/13/bin/pgsqlchk
log_on_failure += USERID
disable = no
only_from = 0.0.0.0/0
per_source = UNLIMITED
}

sudo bash -c 'echo "pgsqlchk 23267/tcp # pgsqlchk" >> /etc/services'
sudo systemctl restart xinetd

# Check if service is working
telnet 127.0.0.1 23267

Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
HTTP/1.1 206 OK
Content-Type: Content-Type: text/plain
Standby
Connection closed by foreign host.

Execute on HaProxy following actions

# Install HaProxy
sudo apt-get install haproxy -y 

sudo vi /etc/hosts
Add pi6 192.168.2.106
Add pi7 192.168.2.107

sudo vi /etc/haproxy/haproxy.cfg  
  
global  
    maxconn 100  
   
defaults  
    log global  
    mode tcp  
    retries 2  
    timeout client 30m  
    timeout connect 4s  
    timeout server 30m  
    timeout check 5s  
   
listen stats  
    mode http  
    bind *:10000  
    stats enable   
    stats refresh 10s
    stats uri /
   
listen Postgres
    bind *:5432 
    option httpchk  
    http-check expect status 200  
    default-server inter 3s fall 3 rise 2 on-marked-down shutdown-sessions  
    server pi6 pi6:5432 maxconn 100 check port 23267  
    server pi7 pi7:5432 maxconn 100 check port 23267  
   
systemctl restart haproxy  

Check HaProxy

# Install postgres client
sudo apt-get install postgresql-client

# Start psql client
psql -h localhost -U postgres  
  
postgres=# select pg_is_in_recovery();  
pg_is_in_recovery  
-------------------  
f  
(1 row)

Check HaProxy portal http://192.168.2.107:5000

Too bad one of my webservers crashed (Solid state disk failed) 3 days ago. I have roll in a new server and migrated all websites to this new server. If you miss something, please let me known.

I also updated the following software:
– Debian to buster
– WordPress to 5.4.1

My Experia Box v8 worked fine last 3 years but now it is failing every few days. All inbound traffic is then blocked (my websites are not accessible anymore) because it can not reach the KPN update server. See below TR069 error. If this occur the router blocks automatic all inbound traffic, preventing any access to my servers. I called the KPN helpdesk and they are willing to replace my old Expiria Box v8 with a v10. Looking forward to receive this new router as soon as possible.

Update 04-01-2018:
I received a new router. Too bad they sent a v8 version and not the promised v10. So i called the service desk again. They promised me again to send a v10, next week.

Update 09-01-2018:
Today i received the Experia box v10. Installed it directly. So now all services are back to normal 🙂

01/02/2019 12:33:39 TR069:Inform Fail!!(Invalid URL or ACS unreachable)
01/02/2019 12:33:39 TR069:Remove host rijswijk1.cust.kpn.net dns record.
01/02/2019 12:33:39 TR069:Sending 1 BOOT inform.

Dear friends, Last 10 years i monitor my website traffic with Google Analytics. See below chart. My website processed more then 194 thousand visitors and 2.7 million page views. That’s really great! Thanks!

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PlaatSoft software (PlaatSign and PlaatEnergy) runs on two Raspberry Pi’s in a Dutch Church “De Oostpoort” in Gouda. The created information system will provide church visitors realtime information about the energy use and energy production (more then 100 solar panels are installed on the roof) of the church building.