October 16, 2017
Arista EOS EAPI – Application Programmable Interface
by Pablo Narváez
NETWORK AUTOMATION
Network automation is usually associated with doing things more quickly which is true, but it’s not the only reason why we should adopt it.
Network administrators usually touch the CLI to make changes on the network. Things get messy when there’s more than one administrator in a multi-vendor environment: Chances for human error are increased when different admins try to make changes on the network using different CLI/tools at the same time.
Replacing manual changes with standardized configuration management tools for network automation help achieve more predictable behavior and minimize “the human error factor”.
Network automation is the use of IT controls to supervise and carry out every-day network management functions. These functions can range from basic network mapping and device discovery to network configuration management and the provisioning of virtual network resources.
Network automation is a powerful and flexible enabler to:
● Efficiently automate repetitive manual operational tasks
● Answer open questions and resolve nonfeasible tasks
● Enable tailored solutions and architectures beyond standard features
Through a step-by-step approach and thanks to many open source examples made available, network automation is easy to adopt in your network today.
Just keep in mind:
“With network automation, the point is to start small, but think through what else you may need in the future.” – Network Programmability by Jason Edelman; Scott S. Lowe; Matt Oswalt
ARISTA EAPI
Introduction
Arista EOS offers multiple programmable interfaces for applications. These interfaces can be leveraged by applications running on the switch, or external to EOS.
The Extensible API (eAPI) allows applications and scripts to have complete programmatic control over EOS, with a stable and easy to use syntax. It also provides access to all switch state.
Once the API is enabled, the switch accepts commands using Arista’s CLI syntax, and responds with machine-readable output and errors serialized in JSON, served over HTTP.
Configuring the Extensible API Interface
One of the benefits about working with Arista EOS eAPI is the ability to script with JSON-RPC. A network administrator can get machine-friendly data from the switch using CLI syntax.
In this post, I will show you the use of eAPI with a simple example using Python.
First, we need to activate the eAPI in each switch. To enable it, we need to bring up the API virtual interface.
leaf01#conf ter leaf01(config)#management api http-commands leaf01(config-mgmt-api-http-cmds)#no shutdown leaf01(config-mgmt-api-http-cmds)#
eAPI requires a username and password to be configured. This is a regular username setup on global configuration:
leaf01#conf ter leaf01(config)#username admineapi secret arista
Default configuration for eAPI uses HTTPS on port 443. Both the port and the protocol can be changed.
leaf01#conf ter leaf01 (config)#management api http-commands leaf01(config-mgmt-api-http-cmds)#protocol ? http Configure HTTP server options https Configure HTTPS server options unix-socket Configure Unix Domain Socket leaf01(config-mgmt-api-http-cmds)#protocol http ? localhost Server bound on localhost port Specify the TCP port to serve on <cr> leaf01(config-mgmt-api-http-cmds)#protocol http port ? <1-65535> TCP port leaf01(config-mgmt-api-http-cmds)#protocol http port 8080 leaf01(config-mgmt-api-http-cmds)#
NOTE: When configuring a non-default http/https pot under “protocol”, that port needs to be manually added to an updated version of the switch´s control-plane access-list to permit remote access.
To verify that the eAPI is running use the following command:
leaf01#show management api http-commands Enabled: Yes HTTPS server: running, set to use port 443 HTTP server: shutdown, set to use port 80 Local HTTP server: shutdown, no authentication, set to use port 8080 Unix Socket server: shutdown, no authentication VRF: default Hits: 0 Last hit: never Bytes in: 0 Bytes out: 0 Requests: 0 Commands: 0 Duration: 0.000 seconds SSL Profile: none QoS DSCP: 0 URLs ------------------------------------- Ethernet4 : https://172.16.0.2:443 Ethernet5 : https://172.16.0.14:443 Loopback0 : https://10.0.1.21:443 Loopback1 : https://10.0.2.1:443 Vlan11 : https://192.168.11.2:443 Vlan4094 : https://172.16.254.1:443
In the output shown above notice the URLs, we are going to need them to access the switch eAPI through HTTP/HTTPS.
USING ARISTA EAPI
There are two methods of using the eAPI:
- Web access
- Programming
eAPI Web Access
The eAPI uses the lightweight, standardized protocol JSON-RPC 2.0 to communicate between your program (the client) and the switch (the server).
To explore the API, point your web browser to https://myswitch after enabling the API interface on the switch.
NOTE: “myswitch” refers to the IP address of the switch you want to configure. To select the appropriate IP address, choose one of the URLs displayed in the command output shown above.
This web-app lets you interactively explore the protocol, return values and model documentation.
The way it works is by sending a JSON-RPC request via an HTTP POST request to https://myswitch/command-api from the client, the request encapsulates a list of CLI commands it wishes to run and the switch replies with a JSON-RPC response containing the result of each CLI command that was executed. The commands in the request are run in order on the switch. After the switch has executed all commands, it exits back to unprivileged mode. If any of the commands emit an error, no further commands from that request are executed, and the response from the switch will contain an error object containing the details of the error that occurred.
To test the eAPI via web browser, let’s try a common command like “show version”:
See the command response in the Response Viewer window.
You can try other commands available in CLI. Check the full list of CLIs supported commands and the corresponding output data entries definition in the top right corner in the “Command Documentation” tab.
Easy to use, right? While the web interface is useful for testing eAPI, it’s not really designed to be a day-to-day function. For a more robust, scalable and complete eAPI experience, the use of the Programming interface is recommended.
eAPI Programming Interface
When using the programming interface to communicate with the switches, we need to read the JSON formatted output. To do so, we are going to add JSON libraries to our environment. For this lab, we have a dedicated Ubuntu Linux server (client) to download the JSON/Python libraries.
NOTE: You don’t need to have an external PC to run the JSON/Python libraries, you can run scripts on the Arista switch itself since all the required JSON libraries are part of the base EOS build.
To enable JSON for use in Python, we need to download the libraries to the Linux server.
superadmin@server00-eapi:~$ sudo apt-get install python-pip superadmin@server00-eapi:~$ sudo pip install jsonrpclib
This is all we need to communicate with the eAPI.
Now we need to create and run a python script to request some information to the switch. To do so, I will use a really simple example to retrieve the output of “show version”.
#!/usr/bin/python from jsonrpclib import Server switch = Server(http://admineapi:arista@192.168.11.2/command-api) response = switch.runCmds(1, [“show version”]) print response
In order to create and run your own Python scripts the use of an IDE (Integrated Development Environment) is strongly recommended. An IDE is a software suite that consolidates the basic tools developers need to write and test software. Typically, an IDE contains a code editor, a compiler or interpreter (Python uses an interpreter) and a debugger that the developer accesses through a single graphical user interface (GUI). There are several IDEs available, please check the following link that contains a review of the most popular ones:
Python Integrated Development Environments
Let’s take a closer look at the script.
This line defines the target (switch). It is broken down as a URL with the following format:
<protocol>://<username>:<password>@<hostname or ip-address>/command-api
The “/command-api” must always be present when using eAPI.
You cannot abbreviate any CLI command and the number “1” in the command is the eAPI version which must always be 1.
Now let’s run the script.
superadmin@server00-eapi:~/scripting$ python hello.py
[{u’memTotal’: 1893352, u’internalVersion’: u’4.17.5M-4414219.4175M’, u’serialNumber’: u”, u’systemMacAddress’: u’52:54:00:97:ea:40′, u’bootupTimestamp’: 1505842331.32, u’memFree’: 583364, u’version’: u’4.17.5M’, u’modelName’: u’vEOS’, u’isIntlVersion’: False, u’internalBuildId’: u’d02143c6-e42b-4fc3-99b6-97063bddb6b8′, u’hardwareRevision’: u”, u’architecture’: u’i386′}]
That may seem like gibberish at first glance, but it’s actually a JSON-formatted set of key-value pairs.
This is the same output, but spaced apart to line it up into more human readable format:
[{
u'memTotal': 1893352,
u'internalVersion': u'4.17.5M-4414219.4175M',
u'serialNumber': u'',
u'systemMacAddress': u'52:54:00:97:ea:40',
u'bootupTimestamp': 1505842331.32,
u'memFree': 583364,
u'version': u'4.17.5M',
u'modelName': u'vEOS',
u'isIntlVersion': False,
u'internalBuildId': u'd02143c6-e42b-4fc3-99b6-97063bddb6b8',
u'hardwareRevision': u'',
u'architecture': u'i386'
}]
Now that we have the key-value pairs, we can reference them to pull out the desired information… this is where the magic happens.
Basically, we have bulk data, so we need an automated way to retrieve the information.
To so, change the script to extract just the value-pair that you need. The format is:
Response[0][“key-name”]
In the next example, I will request the system MAC Address, the EOS version and the total physical memory; all other information will not be displayed.
superadmin@server00-eapi:~/scripting$ cat hello.py #!/usr/bin/python from jsonrpclib import Server switch = Server(http://admineapi:arista@192.168.11.2/command-api) response = switch.runCmds(1, [“show version”]) print “The system MAC address is:”, response[0][“systemMacAddress”] print “The system version is:”, response[0][“version”] print “The total physical memory is:”, response[0][“memTotal”]
This is the result of running the script:
superadmin@server00-eapi:~/scripting$ python hello.py The system MAC address is: 52:54:00:97:ea:40 The system version is: 4.17.5M The total physical memory is: 1893352
Just imagine how you could use this tool compared to the closed vendor-specific monitoring apps, the eAPI provides you with the desired information the way you want it when you want it… You can even create reports and verify compliance with some advanced scripting so this is the flexibility that a programmable operating system provides.
Complex functions require a more sophisticated script. One such example is device provisioning. For deployment automation, you can send multiple commands at once to configure the switch , please see the example below.
#!/usr/bin/python from jsonrpclib import Server switch = Server(http://admineapi:arista@192.168.11.2/command-api) for x in range (10, 19): response = switch.runCmds(1, [ “enable”, “configure”, “interface ethenet2” + str(x), “description [GAD Eth-“ + str(x) + “]”], “json”) print “Done.”
Some commands may require input. This can be accomplished by surrounding the command with curly braces and adding the “cmd” and “input” keywords using the following format:
#!/usr/bin/python from jsonrpclib import Server switch = Server(http://admineapi:arista@192.168.11.2/command-api) response = switch.runCmds(1, [ {“cmd”: “enable”, “input”: “arista”}, “configure”, “interface ethenet2”, “description I can code!”], “json”)
The Arista eAPI (and the API of any other programmable NOS for that matter) is a tremendously powerful tool that puts the very concept of Software Defined Networking within easy reach. The ability to issue CLI commands remotely through scripts is one of the major benefits of network automation and programmable infrastructure.
You can always check my github repository to download the configuration files.
