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.