Getting Started
Overview
The YANG Development Kit (YDK) is a software development tool, which provides API for building applications based on YANG models. The main goal of YDK is to reduce the learning curve of YANG data models by expressing the model semantics in an API and abstracting protocol/encoding details. YDK is composed of a core package that defines services and providers, plus one or more module bundles that are based on YANG models.
Backward Compatibility
The Python YDK-0.8.6 core package is compatible with all model bundles generated previously with ydk-gen releases starting from 0.7.3. However the YDK-0.8.6 generates slightly different code and model API comparing to YDK-0.8.4. The YDK-0.8.6 generated code is not compatible with YDK-0.7.2 and earlier bundle packages due to changes in modeling and handling YList objects.
NOTE. Starting from release 0.8.5 the YDK does not support Python2 interpreter as it was deprecated.
Docker
A docker image is automatically built with the latest ydk-gen installed. This be used to run ydk-gen without installing anything natively on your platform.
To use the docker image, install docker on your system and run the below command. See the docker documentation for more details:
docker run -it ydksolutions/ydk-gen:0.8.6.6
System Requirements
The YDK is currently supported on the following platforms including native installations, virtual machines, and docker images:
Linux Ubuntu Xenial (16.04 LTS), Bionic (18.04 LTS), Focal (20.04 LTS), and Jammy (22.04 LTS)
Linux CentOS versions 7 and Centos Stream 8 (Centos 8.x has been EOL as of December 31 of 2021)
Linux RHEL version 7.x and 8.x
MacOS up to 11.7.2 (Big Sur)
On Windows 10 the Linux virtual machine can run using Windows Subsystem for Linux (WSL); check this for virtual machine installation procedure. The YDK has been tested in such environment on Ubuntu Bionic (18.04 LTS) and Focal (20.04 LTS) images obtained from Microsoft Store.
On supported platforms the YDK can be installed using Installation Script. On other platforms the YDK should be installed manually Building from source. For both the methods the user must install git package prior to the installation procedure.
All YDK core components are based on C and C++ code. These components compiled using default compilers for the supported platform. Corresponding binaries, libraries, and header files are installed in default locations, which are /usr/local/bin, /usr/local/lib, and /usr/local/include. The user must have sudo access in order to install YDK core components to these locations. Make sure the sudo package is installed on your platform prior to the YDK installation procedure.
Core Installation
Installation Script
For YDK installation it is recommended to use script install_ydk.sh from ydk-gen git repository. The script detects platform OS, installs all the dependencies and builds complete set of YDK components for specified language. The user must have sudo access to these locations.
If the script installs any YDK component, it also creates an environment activation file ‘.env’ in the ‘ydk-gen’ directory, which can be used to activate YDK runtime environment identical to the installation environment. To activate YDK runtime environment simply run this command once in bash shell:
cd ydk-gen
source .env
The YDK extensively uses Python scripts for building its components and model API packages (bundles). In order to isolate YDK Python environment from system installation, the script can build Python3 virtual environment. If built, the user must manually activate virtual environment when generating model bundles and/or running YDK based application. By default the Python virtual environment is installed under $HOME/venv directory. If user has different location, the PYTHON_VENV environment variable should be set to that location.
When installing YDK for Python programming language, the third party dependencies and C++ packages must be installed first. This step requires sudo/root access to the installation platform. Here is simple example of core YDK installation for Python programming language with virtual environment:
git clone https://github.com/CiscoDevNet/ydk-gen.git
cd ydk-gen
export YDKGEN_HOME=`pwd` # optional
export PYTHON_VENV=$HOME/ydk_vne # optional
./install_ydk.sh --cpp --core --venv
./install_ydk.sh --py --core --venv
The script also allows to install individual components like dependencies, core, and service packages for specified programming language or for all supported languages. Full set of script capabilities could be viewed like this:
./install_ydk.sh --help
usage: install_ydk [ {--cpp|--py|--go|--all} ] [-c] [-s gnmi] [-h] [-n] [-v]
Options and arguments:
--cpp install YDK for C++ programming language;
requires sudo access for dependencies and libraries installation
--go install YDK for Go programming language
--py|--python install YDK for Python programming language
--all install YDK for all available programming languages;
requires sudo access for dependencies and libraries installation
-v|--venv create python virtual environment
-c|--core install YDK core package
-s|--service gnmi install gNMI service package
-n|--no-deps skip installation of dependencies;
applicable only with --cpp and --all options
-h|--help print this help message and exit
Environment variables:
YDKGEN_HOME specifies location of ydk-gen git repository;
if not set, $HOME/ydk-gen is assumed
PYTHON_VENV specifies location of python virtual environment;
if not set, $HOME/venv is assumed
GOROOT specifies installation directory of go software;
if not set, /usr/local/go is assumed
GOPATH specifies location of go source directory;
if not set, $HOME/go is assumed
C_INCLUDE_PATH location of C include files;
if not set, /usr/local/include is assumed
CPLUS_INCLUDE_PATH location of C++ include files;
if not set, /usr/local/include is assumed
CMAKE_LIBRARY_PATH Location of Python shared libraries;
if not set, default system library location is assumed
If user environment is different from the default one (different Python installation or different location of libraries), then building from source method should be used.
Building from source
Environment variables
In some OS configurations during YDK package installation the cmake fails to find C/C++ headers for previously installed YDK libraries. In this case the headers file location must be specified explicitly (in below commands the default location is shown):
export C_INCLUDE_PATH=/usr/local/include
export CPLUS_INCLUDE_PATH=/usr/local/include
When non-standard Python installation is used or there are multiple installations of Python on the platform, the PATH and CMAKE_LIBRARY_PATH environment variables must be set accordingly in order for the installation scripts to pick up correct Python binaries and shared libraries.
Installing third party dependencies
If user platform is supported one, it is recommended to use ydk-gen/install_ydk.sh script. The script will also install Python virtual environment in default or specified location:
# Clone ydk-gen from GitHub
git clone https://github.com/CiscoDevNet/ydk-gen.git
cd ydk-gen
# Define optional environment variables and install dependencies
export YDKGEN_HOME=`pwd` # optional
export PYTHON_VENV=$HOME/ydk_venv # optional
./install_ydk.sh -v # also builds Python virtual environment and .env file
For unsupported platforms it is recommended to follow logic of ydk-gen/test/dependencies-* scripts.
Installing core components
Please follow this procedure to install YDK core components for Python apps development:
# Activate runtime environment
source .env
# Generate and install YDK core library
python3 generate.py -is --core --cpp
# Generate and install Python core package
python3 generate.py -i --core
Adding gNMI Service
In order to enable YDK support for gNMI protocol, which is optional, the user need install third party software and YDK gNMI service package.
gNMI Service installation
Here is simple example, how gNMI service package for Python could be added:
cd ydk-gen
./install_ydk.sh --cpp --service gnmi --venv # requires sudo access
./install_ydk.sh --py --service gnmi --venv
gNMI runtime environment
When YDK is installed using ‘install_ydk.sh’ script, the runtime environment is set by running ‘source .env’ in bash shell. The below information is applicable only when YDK is installed manually, which is not recommended.
There is an open issue with gRPC on Centos/RHEL, which requires an extra step before running any YDK gNMI application. See this issue on GRPC GitHub for details. As a workaround, the YDK based application runtime environment must include setting of LD_LIBRARY_PATH variable:
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib:/usr/local/lib64
Bundle Installation
Quick installation
You can install the latest model packages from Python package index. Note that Python index does not have this release, therefore make sure the Python core package for this release is already installed prior to bundle installation. Make sure to activate Python virtual environment prior to package installation. When installing a bundle package from Python index, all dependent packages installed automatically. The installation of the ydk-models-cisco-ios-xr and/or ydk-models-cisco-ios-xe bundle(s) (depending on whether you’re developing application for IOS XR or IOS XE platform) automatically installs all other related packages (ydk, openconfig and ietf packages):
pip install ydk-models-cisco-ios-xr
pip install ydk-models-cisco-ios-xe
Alternatively, you can perform a partial installation. If you prefer to install only the openconfig bundle and its dependencies (ydk and ietf packages), execute:
pip install ydk
pip install ydk-models-openconfig
If you want install only the ietf bundle and its dependencies (ydk package), execute:
pip install ydk
pip install ydk-models-ietf
To enable gNMI Service support in Python based application, install package:
pip install ydk-service-gnmi
Installing from source
Once you have installed the ydk core package, you can install one or more model bundles. Note that some bundles have dependencies on other bundles. Those dependencies are already captured in the bundle package. Make sure you install the desired bundles in the order below. To install the ietf bundle from ydk-gen execute:
# Navigate to ydk-gen directory and activate runtime environment
cd ydk-gen
source .env # if not ran previously
# Generate and install the bundle
python3 generate.py --bundle profiles/bundles/ietf_0_1_6.json -i
To install the openconfig bundle, execute:
# Navigate to ydk-gen directory and activate runtime environment
cd ydk-gen
source .env # if not ran previously
# Generate and install the bundle
python3 generate.py --bundle profiles/bundles/openconfig_0_1_9.json -i
To install the cisco-ios-xr bundle, execute:
# Navigate to ydk-gen directory and activate runtime environment
cd ydk-gen
source .env # if not ran previously
# Generate and install the bundle
python3 generate.py --bundle profiles/bundles/cisco-ios-xr-6_7_4_post1.json -i
Generate YDK components
Generation script
All the YDK components/packages can be generated by using Python script generate.py. To get all of its options run:
cd ydk-gen
python3 generate.py --help
usage: generate.py [-h] [-l] [--core] [--service SERVICE] [--bundle BUNDLE]
[--adhoc-bundle-name ADHOC_BUNDLE_NAME]
[--adhoc-bundle ADHOC_BUNDLE [ADHOC_BUNDLE ...]]
[--generate-meta] [--generate-doc] [--generate-tests]
[--output-directory OUTPUT_DIRECTORY] [--cached-output-dir]
[-p] [-c] [-g] [-v] [-o]
Generate YDK artifacts:
optional arguments:
-h, --help show this help message and exit
-l, --libydk Generate libydk core package
--core Generate and/or install core library
--service SERVICE Location of service profile JSON file
--bundle BUNDLE Location of bundle profile JSON file
--adhoc-bundle-name ADHOC_BUNDLE_NAME
Name of the adhoc bundle
--adhoc-bundle ADHOC_BUNDLE [ADHOC_BUNDLE ...]
Generate an SDK from a specified list of files
--generate-meta Generate meta-data for Python bundle
--generate-doc Generate documentation
--generate-tests Generate tests
--output-directory OUTPUT_DIRECTORY
The output directory where the sdk will get created.
--cached-output-dir The output directory specified with --output-directory
includes a cache of previously generated gen-
api/<language> files under a directory called 'cache'.
To be used to generate docs for --core
-p, --python Generate Python SDK
-c, --cpp Generate C++ SDK
-g, --go Generate Go SDK
-v, --verbose Verbose mode
-o, --one-class-per-module
Generate separate modules for each python class
corresponding to YANG containers or lists.
Build model bundle profile
The first step in using ydk-gen is either using one of the already built bundle profiles or constructing your own bundle profile, consisting of the YANG models you are interested to include into the bundle.
Construct a bundle profile file, such as cisco-ios-xr_6_5_3 and specify its dependencies.
A sample bundle profile file is described below. The file is in a JSON format. The profile must define the “name”, “version” and “description” of the bundle, and then the “core_version”, which refers to the version of the YDK core package that you want to use with this bundle. The “name” of the bundle will form part of the installation path of the bundle. All other attributes, like “author” and “copyright”, are optional and will not affect the bundle generation:
"name":"cisco-ios-xr",
"version": "6.5.3",
"core_version": "0.8.6",
"author": "Cisco",
"copyright": "Cisco",
"description": "Cisco IOS-XR Native Models From Git",
The models section of the profile describes sources of YANG models. It could contain combination of elements:
dir - list of relative directory paths containing YANG files
file - list of relative YANG file paths
git - git repository, where YANG files are located
The sample below shows the use of git sources only. Each git source must specify url - git repository URL, and commits list. The specified URL must allow the repository to be cloned without user intervention. Each element in commits list can specify:
commitid - optional specification of a commit ID in string format. If not specified the HEAD revision is assumed.
dir - optional list of relative directory paths within the git repository.
file - optional list of relative *.yang file paths within the git repository.
Only directory examples are shown in this example:
"models": {
"git": [
{
"url": "https://github.com/YangModels/yang.git",
"commits": [
{
"dir": [
"vendor/cisco/xr/653"
]
}
]
},
{
"url": "https://github.com/YangModels/yang.git",
"commits": [
{
"commitid": "f6b4e2d59d4eedf31ae8b2fa3119468e4c38259c",
"dir": [
"experimental/openconfig/bgp",
"experimental/openconfig/policy"
]
}
]
}
]
},
Generate and install model bundle
Generate model bundle using a bundle profile and install it. YDK Runtime environment must be activated prior to these procedures:
python3 generate.py -i --bundle profiles/bundles/<name-of-profile>.json
Check Python packages installed:
pip list | grep ydk
ydk (0.8.6.6)
ydk-models-<name-of-bundle> (0.1.1)
...
Generate “adhoc” bundle
When YANG models available on the hard drive, there is capability to generate small model bundles, which include just few models. It is called an “adhoc” bundle. Such a bundle generated without profile directly from command line. Here is simple example:
python3 generate.py -i --adhoc-bundle-name test --adhoc-bundle \
/opt/git-repos/clean-yang/vendor/cisco/xr/621/Cisco-IOS-XR-ipv4-bgp-oper*.yang \
/opt/git-repos/clean-yang/vendor/cisco/xr/621/Cisco-IOS-XR-types.yang
/opt/git-repos/clean-yang/vendor/cisco/xr/621/Cisco-IOS-XR-ipv4-bgp-datatypes.yang
This will generate a bundle that contains files specified in the –adhoc-bundle option and create Python package ydk-models-test-0.1.0.tar.gz, which has dependency on the base IETF bundle. Note that all dependencies for the bundle must be listed. It is expected that this option will be typically used for generating point model bundles for specific testing. The –verbose option is automatically enabled to quickly and easily let the user see if dependencies have been satisfied.
Generate bundle documentation
In order to generate YDK core and bundles documentation, the –generate-doc option is used when generating core package. Therefore the user should generate all the bundles without the –generate-doc option prior to the documentation generation. For example, the below sequence of commands will generate the documentation for the three python bundles and the python core:
python3 generate.py --bundle profiles/bundles/ietf_0_1_6.json
python3 generate.py --bundle profiles/bundles/openconfig_0_1_9.json
python3 generate.py --bundle profiles/bundles/cisco_ios_xr_6_3_1.json
python3 generate.py --core --generate-doc
NOTE. The documentation generation for bundles can take few hours due to their sizes. If you have previously generated documentation using the –cached-output-dir –output-directory <dir> option, the add-on documentation generation time can be reduced. Adding cisco-ios-xr documentation as an example:
mkdir gen-api/cache
mv gen-api/python gen-api/cache
python3 generate.py --bundle profiles/bundles/cisco_ios_xr_6_6_3.json
python3 generate.py --core --generate-doc --output-directory gen-api --cached-output-dir
Documentation and Support
Pre-generated documentation for YDK-0.8.6 core and model API for IETF and OpenConfig can be found here
Application samples can be found under the samples directory
Hundreds of Python application samples can be found in the samples repository
Join the YDK community to connect with YDK users and developers
Release Notes
The current YDK release version is 0.8.6.6.
YDK is licensed under the Apache 2.0 License.