mongod server under the hood

In the previous post I built mongodb from source. We have an image file from Fedora in elf format with debug information embedded in file.

I already have the code, so use your favorite editor to browse the code. In my case I use VisualStudio code:

I will load the mongod executable with gdb:

Provide initial arguments to mongod with gdb:

set args –dbpath=/home/albertop/mongodb

set breakpoint at main:

then run the beast:

Step the source code. the main() function is embedded in db.cpp file. This file has the entry point for mongod service.

One interesting point is that the thread to serve client request is launched here, the main logic for this thread is contained in transport_layer_asio.cpp file.

Set a breakpoint in start method from this file:

Install mongodb from git in Fedora 29

Although the usual method to install mongodb in Fedora is by using official Fedora repo, I’ll install mongodb from official mongodb github repo.

git clone https://github.com/mongodb/mongo.git

Make sure you have python3 from Fedora, in my case I disabled use of Anaconda.

pip3 install -r etc/pip/compile-requirements.txt

This will install python3 dependencies in your system. Beware of following errors:

gcc: error: /usr/lib/rpm/redhat/redhat-hardened-cc1: No such file or directory
     error: command 'gcc' failed with exit status 1

Use dnf search to look for missing packages.

install sudo dnf install redhat-rpm-config-118-1.fc29.noarch

Python.h missing:

psutil/_psutil_common.c:9:10: fatal error: Python.h: No such file or directory
      #include 
               ^~~~~~
     compilation terminated.
     error: command 'gcc' failed with exit status 1

Again, use dnf search to look for Python.h

sudo dnf install python3-devel-3.7.3-1.fc29.x86_64
sudo dnf install scons
sudo dnf install python3-scons
 sudo dnf install g++

Now, use scons.py, this script is similar to unix build tools automake/autoconf:

python3 buildscripts/scons.py [mongo | all ]

Fix errors from scons stage:

Traceback (most recent call last):
   File "src/mongo/base/generate_error_codes.py", line 45, in 
     from Cheetah.Template import Template
 ModuleNotFoundError: No module named 'Cheetah'

Cheetah was installed at beginning but not found because I was using python3 from Anaconda installation. I removed Anaconda from my path.

Install this package:

sudo dnf install gcc-aarch64-linux-gnu-8.1.1-3.fc29.x86_64

After fixing all build errors you will get mongod binary:

Skipping ranlib for thin archive build/opt/mongo/db/commands/libstandalone.a
 Linking build/opt/mongo/mongod
 Install file: "build/opt/mongo/mongod" as "mongod"
 scons: done building targets.

Beware that using “all” parameter will create mongod, mongo. mongos and mongo-tests. Together, 200 GB will be used by this build.

If you want to install only mongod server:

python3 buildscripts/scons.py mongod

Note that this build will create fedora binary with debug information. That’s ok because next post will walk-through mongod source code.

Add VPN to docker container

Your docker container tries to get access to external VPN.

The docker container will use bridge to talk to host or other containers by default.

It looks like default bridge defaults to localhost so for our case we are going to map new bridge to IP address assigned by VPN.

"Options": {

            "com.docker.network.bridge.default_bridge": "true",

            "com.docker.network.bridge.enable_icc": "true",

            "com.docker.network.bridge.enable_ip_masquerade": "true",

            "com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",

            "com.docker.network.bridge.name": "docker0",

            "com.docker.network.driver.mtu": "1500"

        },

Install wordpress with docker Fedora 29

This is an introduction to docker. Get a docker image prepared by the software owner which you want to install.

In this tutorial we will download from docker hub the image for wordpress and the image for mysql/mariadb server.

The wordpress image has a little bit of magic in it, there is a php and httpd installation packaged with wordpress. There is also a mapping to connect to a mysql server.

The mysql server docker image is a standalone image. This will be used by wordpress docker image.

The docker hub. This is the “App Store” for docker.

Look for docker images here:

https://hub.docker.com/

For instance I will get docker image for wordpress:

Scroll down to read important information of this docker image. You will need to pass values to variables set by the creators of this image.

docker pull mariadb:latest
docker run -e MYSQL_ROOT_PASSWORD=XXX -e MYSQL_USER=wpuser -e MYSQL_PASSWORD=YYY -e MYSQL_DATABASE=wpdb -v /home/albertop/dvol/mysqldir/:/var/lib/mysql --name wordpressdb -d mariadb
docker pull wordpress:latest
docker run -e WORDPRESS_DB_USER=wpuser -e WORDPRESS_DB_PASSWORD=YYY -e WORDPRESS_DB_NAME=wpdb -p 80:80 -v /home/albertop/dvol/htmldir/:/var/www/html --link wordpressdb:mysql --name wpcontainer -d wordpress

Install docker Fedora 29

docker is available in official fedora repo. However, I recommend to use rpms directly from docker site:

https://download.docker.com/linux/fedora/29/

From here download rpms for:

docker-ce
docker-ce-client
containerd.io

Disable/uninstall sssd as this package will prevent to rpm to create docker group and usermod will fail.

containerd.io will not be recognized by rpm when installing docker-ce. Use
–-no-deps option for rpm when installing docker-ce.