Measure Replication Delay with Percona Toolkit Heartbeat (pt-heartbeat)

Replication lag occurs when the slave cannot keep up with the changes being made on the master instance. The reasons for a lag can be network congestion, poor performance on the slave or service interruptions of the slave mechanism, leading to a large pile of work to be catched up by the slave. When you use SHOW SLAVE STATUS you can monitor the current delay, which is indicated in the Seconds_Behind_Master: 0column. Ideally, this value is zero, but the smallest granularity you get for this delay counter is one second.

Percona offers a tool that allows measuring the delay more accurately, by writing timestamps in the master database and calculate the difference when they arrive at the slave: pt-heartbeat

On the Master

Create a dedicated database schema called percona and add the following table. 

CREATE TABLE IF NOT EXISTS `percona`.`heartbeat` (
    ts                    varchar(26) NOT NULL,
    server_id             int unsigned NOT NULL PRIMARY KEY,
    file                  varchar(255) DEFAULT NULL,    -- SHOW MASTER STATUS
    position              bigint unsigned DEFAULT NULL, -- SHOW MASTER STATUS
    relay_master_log_file varchar(255) DEFAULT NULL,    -- SHOW SLAVE STATUS
    exec_master_log_pos   bigint unsigned DEFAULT NULL  -- SHOW SLAVE STATUS

Then you can launch the script on the master, where it will write new timestamps periodically as long as the script is running.

pt-heartbeat -D percona --update --utc h=,u=root,p=SECRET,P=3306

The -D flag specifies the database schema where the table for the heartbeat data is stored. The –update command is needed on the master for updating the table and the last part is the DSN, which specifies host address, user name and password. Very important is the UTC flag –utc, that ensures that the timestamps will be interpreted as UTC, regardless of the timezone setting. 

On the Slave

Create a user for reading the replicated heartbeat table like this:


Then you can run the script and point it to the slave. It will output precise delay counts in fractions of seconds

pt-heartbeat h=,u=percona_checksum,p=SECRET,P=3306 -D percona --monitor --utc --master-server-id 1

Notice the different DSN, the –monitor flag and the master-server id, which needs to be the one of your master of course. You need this because the tool supports hierarchies of masters and therefore you would need to know which one is to be considered.


The results will look similar to this

0.09s [  0.00s,  0.00s,  0.00s ]
0.02s [  0.20s,  0.00s,  0.00s ]
0.09s [  0.00s,  0.00s,  0.00s ]
0.03s [  0.02s,  0.00s,  0.00s ]
0.09s [  0.01s,  0.00s,  0.00s ]
0.09s [  0.01s,  0.00s,  0.00s ]
0.09s [  0.01s,  0.00s,  0.00s ]
0.08s [  0.01s,  0.00s,  0.00s ]
0.08s [  0.01s,  0.00s,  0.00s ]
0.10s [  0.01s,  0.00s,  0.00s ]
0.12s [  0.02s,  0.00s,  0.00s ]
0.08s [  0.01s,  0.00s,  0.00s ]
0.11s [  0.02s,  0.00s,  0.00s ]
0.08s [  0.02s,  0.00s,  0.00s ]
0.09s [  0.02s,  0.00s,  0.00s ]
0.08s [  0.02s,  0.00s,  0.00s ]
0.08s [  0.03s,  0.01s,  0.00s ]

The output is the current delay followed by moving averages over 1m, 5m and 15m, as you might know from your favorite OS already.

Have a look at the official documentation, there is a lot of options available. 



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Setup AWS MySQL 5.6 Aurora as a Slave for an external Master with SSL

Setting up Aurora as a slave for an external MySQL server that acts as the master is a bit tricky. Of course we want a secured connection. For this reason we need to create client certificates to be used by AWS RDS. The steps below should work for RDS as well. 

Generate and Sign  the Certificates

The process is actually simple, but AWS is picky how you generate the certificates. I was using a SHA flag that was accepted by a regular MySQL 5.6 instance, but caused a cryptic (pun intended) MySQL 2026 Generic SSL error and it was quite hard to find the source.  Also note that you need to have different common names (CN) for all three certificate pairs. They do not necessarily need to fit the actual domain name, but they need to be different. 

First we need to create the certificate authority that can sign the keys

# Generate a certificate authority key pair
openssl genrsa 2048 > ca-key.pem
# Notice the CN name. It needs to be different for all of the three key pairs that we create!
openssl req -new -x509 -nodes -days 3600 -key ca-key.pem -out ca.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=ca.mysql"

Then create the server key pair

#Generate a server key. Note again the different CN
openssl req -newkey rsa:2048 -days 3600 -nodes -keyout server-key.pem -out server-req.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=server.mysql"
# Convert the format
openssl rsa -in server-key.pem -out server-key.pem
# Sign it
openssl x509 -req -in server-req.pem -days 3600 -CA ca.pem -CAkey ca-key.pem -set_serial 01 -out server-cert.pem

Finally we generate a client certificate and its key. You can repeat these steps to generate multiple certificates for clients

# Again, note the CN
openssl req -newkey rsa:2048 -days 3600 -nodes -keyout client-key.pem -out client-req.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=client.mysql"
# Convert
openssl rsa -in client-key.pem -out client-key.pem
# Sign
openssl x509 -req -in client-req.pem -days 3600 -CA ca.pem -CAkey ca-key.pem -set_serial 01 -out client-cert.pem
# Verify
openssl verify -CAfile ca.pem server-cert.pem client-cert.pem

Now we have all the certs we need.

Master Setup

The setup is pretty standard. Add the server certificates to the MySQL configuration of your master and restart.

# SSL Server Certificate

Then create a user for the slave


Slave Setup

On AWS you do not have SUPER() privileges, but can use stored procedures provided by Amazon to setup the slave.

Start fresh by removing old records. If there was no previous setup, there might be an error.

CALL mysql.rds_remove_binlog_ssl_material;
CALL mysql.rds_reset_external_master;

Now you need to pass the client certificate data as a JSON to AWS Aurora.

CALL mysql.rds_import_binlog_ssl_material('{"ssl_ca":"-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----\n","ssl_cert":"-----BEGIN CERTIFICATE-----
-----END CERTIFICATE-----\n","ssl_key":"-----BEGIN RSA PRIVATE KEY-----
-----END RSA PRIVATE KEY-----"}');

A message that the SSL data was accepted will appear if you pasted the certificate, the key and the CA certificate correctly.

Finally, start the replication and check the status

CALL mysql.rds_start_replication;

Tests and Troubleshooting

On the master, you can check if the slave even tries to connect for instance with tcpdump. In the example below the IP would be the AWS gateway address as seen by your firewall.

sudo tcpdump src host -vv


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Grafana and InfluxDB with SSL inside a Docker Container

Self-signed SSL certificates

On the host, create a directory for storing the self signed SSL certificates. This directory will be mounted in the Grafana container as well as in the InfluxDB container to /var/ssl . Create the self signed SSL certificates as follows:

mkdir -p /docker/ssl
cd /docker/ssl/
# Generate a private key
openssl genrsa -des3 -out server.key 1024
# Generate CSR
openssl req -new -key server.key -out server.csr
# Remove password
openssl rsa -in server.key -out server.key
# Generate self signed cert
openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt
# Set permissions
sudo chmod 644 server.crt
sudo chmod 600 server.key

Next, create a config directory and create individual configuration files for Grafana and InfluxB: mkdir conf 


In the file ./conf/grafana/defaults.ini set the protocol to https and provide the paths to the mounted ssl directory in the container.

#################################### Server ##############################
# Protocol (http, https, socket)
protocol = https
# https certs & key file
cert_file = /var/ssl/server.crt
cert_key = /var/ssl/server.key


The file ./conf/influxdb/influxdb.conf is also pretty simple. Add a [http] category and add the settings:

  dir = "/var/lib/influxdb/meta"
  dir = "/var/lib/influxdb/data"
  engine = "tsm1"
  wal-dir = "/var/lib/influxdb/wal"
  https-enabled = true
  https-certificate ="/var/ssl/server.crt"
  https-private-key ="/var/ssl/server.key"


You can set environment variables in env files  for the services.





Docker Compose

Now you can launch the service by using docker-compose up  for the following file. Note

version: '2'

        image: influxdb:latest
        container_name: influxdb
            - "8083:8083"
            - "8086:8086"
            - "8090:8090"
            - 'env.influxdb'
            - data-influxdb:/var/lib/influxdb
            - /docker/ssl:/var/ssl
            - /docker/conf/influxdb/influxdb.conf:/etc/influxdb/influxdb.conf

        image: grafana/grafana:latest
        container_name: grafana
            - "3000:3000"
            - influxdb
            - 'env.grafana'
            - data-grafana:/var/lib/grafana
            - /docker/ssl:/var/ssl
            - /docker/conf/grafana/defaults.ini:/usr/share/grafana/conf/defaults.ini

Lets Encrypt Setup

If you require valid certificates, you can also use certificates from lets encrypt.

First, create the certificates on the host:

certbot certonly --standalone --preferred-challenges http --renew-by-default -d

Then use this docker-compose file.

version: '2'

        image: influxdb:latest
        container_name: influxdb
            - "8083:8083"
            - "8086:8086"
            - "8090:8090"
            - 'env.influxdb'
            - data-influxdb:/var/lib/influxdb
            - /etc/letsencrypt/live/
            - /etc/letsencrypt/live/
            - /docker/conf/influxdb/influxdb.conf:/etc/influxdb/influxdb.conf

        image: grafana/grafana:latest
        container_name: grafana
            - "3000:3000"
            - influxdb
            - 'env.grafana'
            - data-grafana:/var/lib/grafana
            - /etc/letsencrypt/live/
            - /etc/letsencrypt/live/
            - /docker/conf/defaults.ini:/usr/share/grafana/conf/defaults.ini

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Unbrick a Netgear WNR3500L V2

It finally happened… After experimenting with alternative firmware for my WNR3500L router, I uploaded the wrong version and converted the device into a rather expensive paperweight. After some searching, I found this page, explaining how to revitalize the router by using a USB-TTL converter cable. You can get  (e.g. CP2102 Module Modul USB to TTL Converter) for a few bucks Ebay, but expect a few weeks for the delivery from China.  If you follow the tutorial on the OpenRouters page closely, it should work out quite nicely.

Update: 2018-01-21

It happened again. I flashed an unsupported version of LEDE on the device and it did not want to boot again. I followed the same procedure as described here, but the router was complaining about a version missmatch of the device ID and the image ID. Turns out, I had to explicitly use binary mode for FTP. Here are the steps again.

  1. Connect the serial cables as shown
  2. Make sure router is off
  3. Launch minicom in a terminal and make sure the settings are valid for ttyUSB0
  4. Boot the router and immediately press Ctrl+C in the terminal
  5. Type tftpd in the prompt, the router should start a FTP server on
  6. Open a second terminal, cd into the directory where the firmware is
  7. Make sure its the right version 🙂
  8. Start the FTP client: ftp
  9. Change to binary mode (this is very important): mode binary
  10. Move the file: put FIRMWARE.chr
  11. The router should detect the file and process it
  12. Reboot and enjoy

Connecting a Serial TTYUSB Device to the Router



When you see this message below, you need to abort the boot process.

Willkommen zu minicom 2.7

Optionen: I18n 
Übersetzt am Feb  7 2016, 13:37:27.
Port /dev/ttyUSB0, 17:47:29

Drücken Sie CTRL-A  Z für Hilfe zu speziellen Tasten
Found a Samsung NAND flash with 2048B pages or 128KB blocks; total size 128MB

CFE for WNR3500Lv2 version: v1.0.9
Build Date: Fri May  6 11:54:17 CST 2011 
Init Arena
Init Devs.
Boot partition size = 262144(0x40000)
NFLASH Boot partition size = 524288(0x80000)
et0: Broadcom BCM47XX 10/100/1000 Mbps Ethernet Controller 5.60.136 
CPU type 0x19749: 480MHz
Tot mem: 131072 KBytes

Device eth0:  hwaddr 84-1B-5E-4E-FF-84, ipaddr, mask
        gateway not set, nameserver not set
Checking crc...done.
Loader:raw Filesys:raw Dev:flash0.os File: Options:(null)
Loading: .. 3848 bytes read
Entry at 0x80001000
Closing network.
Starting program at 0x80001000

When pressing Ctrl+C does not work, make sure your minicom settings look like this:

A - Serieller Anschluss      : /dev/ttyUSB0                           |
B - Pfad zur Lockdatei       : /var/lock                              |
C - Programm zur Rufannahme  :                                        |
D - Programm zum Wählen      :                                        |
E - Bps/Par/Bits             : 115200 8N1                             |
F - Hardware Flow Control    : Nein                                   |
G - Software Flow Control    : Nein


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Flashing a OnePlus One from CM to LineageOS

As Cyanogen Inc closed down its operations in December 2016, CyanogenMod was affected too and my OnePlus One (OPO) did not receive updates anymore. This is not ideal, as new and old bugs have will remain. For instance did my phone often not reconnect to the 4G network, when a wifi connection was lost, This was very annoying. For this reason, if was about time to upgrade to a new OS: LineageOS.


LineageOS is a fork of CyanogenMod and contunes the quite successful project for our benefit. LineageOS 14 is compatible with Android 7.1 and very easy to install. These are the steps which I had to follow.

How to Upgrade

  • Create a backup with Helios. Use the Chrome Helium app if the app on your mobile phone refuses to start.
  • Download and install adb
  • Download the TWRP custom ROM: 
  • Download LineageOS. The codename for the OPO is bacon.
  • Download the Google apps mini distribution (stock is too large) here.
  • Enable developer tools and connect the phone with a USB cable
  • Reboot the device with adb: ./adb reboot bootloader 
  • Check if the device is recognized: ./fastboot devices 
  • Enable OEM unlock: fastboot oem unlock 
  • Install the custom rom: fastboot flash recovery twrp-x.x.x-x-bacon.img 
  • Reboot into the new ROM: With the device powered down, hold the Volume Down and Power buttons.

Copy the files to the device

# Lineage
adb push ~/Downloads/OPO-Upgrade/ /sdcard/
# Google Apps
adb push ~/Downloads/OPO-Upgrade/ /sdcard/

Install both zip files by selecting first the LineageOS and then the Google Apps Zip file

Thats it. Reboot and begin with the setup or restore the backup.

Update 28.09.2017

The problem that the phone would not reconnect to 3G/4G again after losing the Wifi signal still persisted with LineageOS. A friend recommended flashing the firmware of the device. After installing the version 2016_1-25_.4.0.1.c7-00011 downloaded from here solved the issue for now. No more connection problems so far

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