My demo, Evolving your APIs, features a custom Apache APISIX plugin. I believe that the process of creating a custom plugin is relatively well-documented. However, I wanted to check the parameters of the
_M.access(conf, ctx)function, especially the
The documentation states:
ctxparameter caches data information related to the request. You can use
core.log.warn(core.json.encode(ctx, true))to output it to
core.log ultimately depends on nginx's logging, and its buffer is limited in size. Thanks to my colleague Abhishek for finding the info. For this reason, the
ctx display is (heavily) truncated. I had to log data bit by bit; however, it was instructive.
ctx parameter is a Lua table. In Lua, table data structures are used for regular indexed access (akin to arrays) and key access (like hash maps). A single
ctx instance is used for each request.
The Apache APISIX engine reads and writes data in the
ctx table. It's responsible for forwarding the latter from plugin to plugin. In turn, each plugin can also read and write data.
I resorted to a custom plugin to conditionally apply rate-limiting in the demo. The custom plugin is a copy-paste of the limit-count plugin. Note that the analysis is done in a specific context. Refrain from assuming the same data is available in your own. However, it should be a good starting point.
Overview of the
The data available in the
ctx parameter is overwhelming. To better understand it, we shall go from the more general to the more particular. Let's start from the overview.
conf_id: either route ID or service ID
proxy_rewrite_regex_uri_capture: data set by the proxy-rewrite plugin.
route_id: route ID the plugin is applied to
route_name: route name the plugin is applied to
real_current_req_matched_path: URI for which matching was done
conf_version: etcd-related revision - see below
var: references the
ctxobject and a cache of data about the request, e.g., URI, method, etc.
matched_route: the route that was matched based on host header/URI and/or
remote_addr; see below
plugins: pairs of plugin/data - see below
matched_route row is a complex data tree that deserves a detailed description.
key: access key in the
orig_modifiedIndex: these attributes are related to etcd and how it stores metadata associated with revisions. Different revisions of a single key are logged in the
pre_revisionfields. The former points to the initial created row ID and is constant throughout the changes, while the latter points to the row ID of the previous value.
Apache APISIX maps them respectively to the
modifiedIndexvalues and uses them for caching. In many places,
created_indexis later assigned to
conf_version- see above.
prev_plugin_config_ver: after a plugin configuration is merged with the route configuration, the current
modifiedIndexis assigned to
prev_plugin_config_ver. It allows saving CPU cycles if one attempts to apply the same plugin config later in the call chain.
update_count: replaced with
has_domain: whether the matched route references an upstream with a domain, e.g.,
http://httpbin.org, or not, e.g.,
orig_plugins: temporary placeholder used if a route has plugins defined directly and reference a plugins config
clean_handlers: list of functions scheduled to be called after a plugin has been created
valuehas keys related to how the route was created, as well as a couple of others:
curl http://apisix:9180/apisix/admin/routes/2 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
"name": "Versioned Route to Old API",
"uris": ["/v1/hello", "/v1/hello/", "/v1/hello/*"],
priority: since we didn't set it, it has a default value 0. Priority is essential when multiple routes match to determine which one to apply.
plugins: references to plugin's function
status: I couldn't find this
plugins value contains plugin-related data in an indexed-based Lua table. Each plugin has two entries: the first (even-indexed) entry contains data related to the plugin in general, e.g., its schema; while the second (odd-index) entry data is related to its configuration in the current route.
My setup has two plugins, hence four entries, but to keep things simpler, I kept only a single plugin in the following diagram:
Key values match directly to the plugin schema and configuration; you can check the whole descriptions directly in the plugin.
A final trick
I initially had issues printing the
ctx table because of the nginx buffer limit and had to do it bit by bit. However, you can print it to a file.
Here's the function, courtesy of my colleague Zeping Bai:
local file, err = io.open("conf/ctx.json", "w+")
if not file then
ngx.log(ngx.ERR, "failed to open file: ", err)
file.write(core.json.encode(ctx, true) .. "\n")
Here's the whole data representation with PlantUML.
In this post, I described the structure of the
ctx parameter in the
access() function. While specific entries vary from configuration to configuration, it gives a good entry point into data manipulated by plugins.
It's also a good reminder that even if you're not fluent in a language or a codebase, you can get quite a lot of information by logging some variables.
To go further: