feat: add warning for data plane writing to etcd

[LiteSun]

Description

When APISIX is running as a data plane, if any ETCD write operations are performed through core.etcd related functions or CLI, warning logs will be printed without blocking the write operations. This functionality will be deprecated in future versions, after which write operations will no longer be allowed.

Mailing list: https://lists.apache.org/thread/gfsooqm4cz6cx2sh7htmqgwlml5kggm2

Scope of Impact

ETCD Write Operations Using core.etcd Related Functions

Example usage:

local core = require("apisix.core")

core.etcd.set("key", "value")

Based on the analysis of the apisix/core/etcd.lua file, the following functions can perform ETCD write operations:

• _M.set
• _M.atomic_set
• _M.push
• _M.delete
• _M.rmdir
• _M.keepalive

For these functions, warning logs will be printed to inform users that this functionality will be deprecated in future versions, after which write operations will no longer be allowed.

ETCD Write Operations Using CLI Created by core.etcd.new()

Example usage:

local core = require("apisix.core")

local etcd_cli = core.etcd.new()
etcd_cli:set("key", "value")

After exporting the CLI, referring to the https://github.com/api7/lua-resty-etcd/blob/master/lib/resty/etcd/v3.lua file, the following operations perform ETCD write operations:

• setnx
• setx
• delete
• rmdir
• grant
• revoke
• keepalive
• set

For these functions, warning logs will be printed to inform users that this functionality will be deprecated in future versions, after which write operations will no longer be allowed.

Timeline

If there are no strong objections on the mailing list, the plan is as follows:

1. Add warning messages in version 3.13.0 without blocking ETCD write operations
2. Provide an adjustment period for users during versions 3.14.0 and 3.15.0, and officially deprecate this functionality in version 3.16.0. Considering the uncertainty in APISIX's release cycle, this functionality will be officially deprecated no later than 6 months after the release of version 3.13.0.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[nic-6443]

block is not a good name in here. block is often used to indicate IO blocking, such as: blocking io and non-blocking io. block_write has a significant ambiguity with the actual function of this function. It is recommended to change it to disable, etc.

[LiteSun]

updated

[ronething]

lgtm