寫點東西吧，懒人。

· ☕ 2 分钟

curl http2

https://http2-explained.haxx.se/en/part11

11.1. HTTP 1.x look-alike

Internally, curl will convert incoming http2 headers to HTTP 1.x style headers and provide them to the user, so that they will appear very similar to existing HTTP. This allows for an easier transition for whatever is using curl and HTTP today. Similarly curl will convert outgoing headers in the same style. Give them to curl in HTTP 1.x style and it will convert them on the fly when talking to http2 servers. This also allows users to not have to bother or care very much with which particular HTTP version that is actually used on the wire.

· ☕ 1 分钟

https://pi3g.com/2019/01/17/envoy-as-http-2-front-proxy-enabling-http-2-for-envoy-aka-h2/

envoy as http 2 front proxy – enabling http 2 for envoy (aka h2)

By Maximilian Batz | 2019-01-17

Out of the box envoy is not configured to set up connections with clients connecting to it with the new HTTP/2.

HTTP/2 is optimized for the modern web, with binary headers, etc. – higher speed.

Since envoy is capable of speaking HTTP/2 to clients, it is a no-brainer to set it up.

· ☕ 1 分钟

Header case

https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2

8.1.2. HTTP Header Fields

HTTP header fields carry information as a series of key-value pairs.
For a listing of registered HTTP headers, see the “Message Header
Field” registry maintained at <https://www.iana.org/assignments/
message-headers>.

Just as in HTTP/1.x, header field names are strings of ASCII characters that are compared in a case-insensitive fashion. However, header field names MUST be converted to lowercase prior to their encoding in HTTP/2. A request or response containing uppercase header field names MUST be treated as malformed (Section 8.1.2.6](https://datatracker.ietf.org/doc/html/rfc7540#section-8.1.2.6)).

· ☕ 6 分钟

Negotiation

HTTP 1.1 plain text Upgrade header

https://http2-explained.haxx.se/en/part5#5.1.-http2-for-existing-uri-schemes

As mentioned already, the existing URI schemes cannot be modified, so http2 must use the existing ones. Since they are used for HTTP 1.x today, we obviously need a way to upgrade the protocol to http2, or otherwise ask the server to use http2 instead of older protocols.

HTTP 1.1 has a defined way to do this, namely the Upgrade: header, which allows the server to send back a response using the new protocol when getting such a request over the old protocol, at the cost of an additional round-trip.

· ☕ 1 分钟

Ubuntu 包溯源

文件来自什么样包 - finding the package a file belongs

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labile@worknode1:/etc/apt/sources.list.d$ dpkg -S /usr/bin/crictl
cri-tools: /usr/bin/crictl

包来自什么源 - How do I find out which repository a package comes from

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apt-cache policy cri-tools

cri-tools:
  Installed: 1.19.0-00
  Candidate: 1.19.0-00
  Version table:
 *** 1.19.0-00 500
        500 https://apt.kubernetes.io kubernetes-xenial/main amd64 Packages
        100 /var/lib/dpkg/status
     1.13.0-01 500
        500 https://apt.kubernetes.io kubernetes-xenial/main amd64 Packages
· ☕ 1 分钟

Cycles per instruction (CPI) :

As we know, all the requests are served by CPU in the form of instruction sets. A single request can translated in to 100’s of instruction sets. Cycles spent per instruction is an important parameter which helps understand where CPU is spending its clock cycles. This metrics can also be expressed in the inverse form, i.e, Instructions per Cycle (IPC).

It is important to note that CPI value signifies the efficiency of instruction processing , but not of the instructions themselves.

· ☕ 1 分钟

https://easyperf.net/blog/2019/02/09/Top-Down-performance-analysis-methodology

In this post I show more formal way to do performance analysis. It’s called Top-down Microarchitecture Analysis Method (TMAM) (Intel® 64 and IA-32 Architectures Optimization Reference Manual, Appendix B.1). In this metodology we try to detect what was stalling our execution starting from the high-level components (like Front End, Back End, Retiring, Branch predictor) and narrowing down the source of performance inefficiencies.

It’s an iterative process with 2 steps:

· ☕ 2 分钟

https://redis.io/topics/acl

ACL

The Redis ACL, short for Access Control List, is the feature that allows certain connections to be limited in terms of the commands that can be executed and the keys that can be accessed. The way it works is that, after connecting, a client is required to authenticate providing a username and a valid password: if the authentication stage succeeded, the connection is associated with a given user and the limits the user has. Redis can be configured so that new connections are already authenticated with a “default” user (this is the default configuration), so configuring the default user has, as a side effect, the ability to provide only a specific subset of functionalities to connections that are not explicitly authenticated.