SRE Book摘录:服务架构



Figure 2-4shows how a user’s request is serviced: first, the user points their browser
to To obtain the corresponding IP address, the user’s device
resolves the address with its DNS server (1). This request ultimately ends up at Goo‐
gle’s DNS server, which talks to GSLB. As GSLB keeps track of traffic load among
frontend servers across regions, it picks which server IP address to send to this user.

The browser connects to the HTTP server on this IP. This server (named the Google
Frontend, or GFE) is a reverse proxy that terminates the TCP connection (2). The
GFE looks up which service is required (web search, maps, or—in this case—Shake‐
speare). Again using GSLB, the server finds an available Shakespeare frontend server,
and sends that server an RPC containing the HTML request (3).

The Shakespeare server analyzes the HTML request and constructs a protobuf con‐
taining the word to look up. The Shakespeare frontend server now needs to contact
the Shakespeare backend server: the frontend server contacts GSLB to obtain the BNS
address of a suitable and unloaded backend server (4). That Shakespeare backend
server now contacts a Bigtable server to obtain the requested data (5).

The answer is written to the reply protobuf and returned to the Shakespeare backend
server. The backend hands a protobuf containing the results to the Shakespeare
frontend server, which assembles the HTML and returns the answer to the user.

This entire chain of events is executed in the blink of an eye—just a few hundred mil‐
liseconds! Because many moving parts are involved, there are many potential points
of failure; in particular, a failing GSLB would wreak havoc. However, Google’s policies
of rigorous testing and careful rollout, in addition to our proactive error recovery methods such as graceful degradation, allow us to deliver the reliable service that our
users have come to expect. After all, people regularly use check if
their Internet connection is set up correctly.

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