Preparing for 3.3.0
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Olof hagsand
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doc/FAQ.md
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doc/FAQ.md
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Frequently Asked Questions - CliXon
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===================================
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Q: What is CliXon?
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------------------
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CliXon is a configuration management tool including CLI generation,
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Yang parser, netconf interface and an embedded databases.
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Q: Why should you use CliXon?
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-----------------------------
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If you want an easy-to-use config frontend based on yang with an open-source license.
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Typically for embedded devices requiring a config interface such as routers and switches.
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Q: What license is available?
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-----------------------------
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The basic license is open-source, GPLv3. Contact authors for commercial license.
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Q: Is CliXon extendible?
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------------------------
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Yes. All application semantics is defined in plugins with well-defined APIs. There are currently three types of plugins: for CLI, for Netconf and for the backend.
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Q: Which language is CliXon implemented in?
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-------------------------------------------
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CliXon is written in C. The plugins are written in C. The CLI
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specification uses cligen (http://cligen.se)
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There is a project for writing plugins in Python. It is reasonable
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simple to spawn an external script from a backend.
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Q: Is CliXon different from Clicon?
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-----------------------------------
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CliXon is a fork of Clicon focussing on Yang specification and XML
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database. The yang support in clicon was grown out of a key-based
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scheme that became more and more complex since it had to translate
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between many different formats. CliXon uses only XML internally.
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The commit transaction mechanism has been simplified too. But CliXon
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is not backward compliant with key-based Clixon applications, such as
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Rost.
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Q: How to best understand CliXon?
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---------------------------------
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Run the ietf yang routing example. It is used in many of the answers below.
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Q: How do you build and install CliXon (and the example)?
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---------------------------------------------------------
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CliXon:
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./configure;
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make;
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sudo make install;
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sudo make install-include
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The example:
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cd example;
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make;
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sudo make install
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Q: What about reference documentation?
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--------------------------------------
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CliXon uses Doxygen for reference documentation.
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Build using 'make doc' and aim your browser at doc/html/index.html or
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use the web resource: http://clicon.org/ref/index.html
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Q: How do you run the example?
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------------------------------
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- Start a backend server: 'clixon_backend -Ff /usr/local/etc/routing.conf'
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- Start a cli session: clixon_cli -f /usr/local/etc/routing.conf
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- Start a netconf session: clixon_netconf -f /usr/local/etc/routing.conf
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Q: Can you run CliXon as docker containers?
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-------------------------------------------
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Yes, the example works as docker containers as well. backend and cli needs a
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common file-system so they need to run as a composed pair.
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cd example/docker
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make docker # Prepares /data as shared file-system mount
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run.sh # Starts an example backend and a cli
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The containers are by default downloaded from dockerhib, but you may
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build the containers locally:
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cd docker
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make docker
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You may also push the containers with 'make push' but you may then consider changing the image name in the makefile.
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Q: How do you change the example?
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---------------------------------
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- routing.conf.local - Override default settings
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- The yang specifications - This is the central part. It changes the XML, database and the config cli.
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- routing_cli.cli - Change the fixed part of the CLI commands
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- routing_cli.c - Cli C-commands are placed here.
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- routing_backend.c - Commit and validate functions.
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- routing_netconf.c - Modify semantics of netconf commands.
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Q: How do you check what is in a database?
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------------------------------------------
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Use clixon_dbctrl. The name of the running or candidate databases are found in the
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configuration file.
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Example:
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> clixon_dbctrl -d /usr/local/var/routing/candidate_db / -p
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/interfaces/interface/eth0/ipv4
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/interfaces/interface/eth0/type bgp
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/interfaces/interface/eth0
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/interfaces/interface/eth0/name eth0
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Each line corresponds to a database entry (node in an XML tree).
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If the node is a leaf, the value appears as the second entry ('bgp' and 'eth0').
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Q: What is validate and commit?
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-------------------------------
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Clixon follows netconf in its validate and commit semantics.
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In short, you edit a 'candidate' configuration, which is first
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'validated' for consistency and then 'committed' to the 'running'
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configuration.
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A clixon developer writes commit functions to incrementaly upgrade a
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system state based on configuration changes. Writing commit callbacks
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is the core functionality of a clixon system.
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Q: How do you write a commit function?
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--------------------------------------
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You write a commit function in routing_backend.c.
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Every time a commit is made, transaction_commit() is called in the
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backend. It has a 'transaction_data td' argument which is used to fetch
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information on added, deleted and changed entries. You access this
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information using access functions as defined in clixon_backend_transaction.h
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Q: How do you check what has changed on commit?
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-----------------------------------------------
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You use XPATHs on the XML trees in the transaction commit callback.
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Suppose you want to print all added interfaces:
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cxobj *target = transaction_target(td); # wanted XML tree
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vec = xpath_vec_flag(target, "//interface", &len, XML_FLAG_ADD); /* Get added i/fs */
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for (i=0; i<len; i++) /* Loop over added i/fs */
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clicon_xml2file(stdout, vec[i], 0, 1); /* Print the added interface */
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You can look for added, deleted and changed entries in this way.
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Q: How do I access the XML tree?
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--------------------------------
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Using XPATH, find and iteration functions defined in the XML library. Example library functions:
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xml_child_each(),
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xml_find(),
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xml_body(),
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clicon_xml2file(),
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xml_apply()
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More are found in the doxygen reference.
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Q: How do you write a CLI callback function?
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--------------------------------------------
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(1) You add an entry in routing_cli.cli
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example("This is a comment") <var:int32>("This is a variable"), mycallback("myarg");
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(2) Then define a function in routing_cli.c
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mycallback(clicon_handle h, cvec *cvv, cg_var *arg)
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where 'cvv' contains the value of the variable and 'arg' contains the
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function parameter 'myarg'.
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Q: What are cg_var and cvec used in CLI callbacks?
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--------------------------------------------------
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Those are 'CLIgen variables' and vector of CLIgen variables.
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They are documented in CLIgen documentation. Some examples on usage is found in the
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routing_cli.c
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Q: How do you write a validation function?
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------------------------------------------
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Similar to a commit function, but instead write the transaction_validate() function.
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Check for inconsistencies in the XML trees and if they fail, make an clicon_err() call.
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clicon_err(OE_PLUGIN, 0, "Route %s lacks ipv4 addr", name);
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return -1;
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The validation or commit will then be aborted.
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Q: How do you use netconf?
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--------------------------
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As an alternative to cli configuration, you can use netconf. Easiest is to just pipe netconf commands to the clixon_netconf application.
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Example:
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echo "<rpc><get-config><source><candidate/></source><configuration/></get-config></rpc>]]>]]>" | clixon_netconf -f /usr/local/etc/routing.conf
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However, more useful is to run clixon_netconf as an SSH
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subsystem. Register the subsystem in /etc/sshd_config:
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Subsystem netconf /usr/local/bin/clixon_netconf
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and then invoke it from a client using
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ssh -s netconf <host>
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Q: How do you use notifications?
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--------------------------------
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The example has a prebuilt notification stream called "ROUTING" that triggers every 10s.
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You enable the notification either via the cli or via netconf:
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cli> notify
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cli> Routing notification
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Routing notification
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...
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> clixon_netconf -qf /usr/local/etc/routing.conf
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<rpc><create-subscription><stream>ROUTING</stream></create-subscription></rpc>]]>]]>
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<rpc-reply><ok/></rpc-reply>]]>]]>
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<notification><event>Routing notification</event></notification>]]>]]>
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<notification><event>Routing notification</event></notification>]]>]]>
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...
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