Replace master/slave with primary/replica

After further feedback I've not updated the images and just made
alterations to the READMEs for mentions of master-slave to
primary-replica

solutions/system_design/scaling_aws/README-zh-Hans.md

@@ -207,7 +207,7 @@
         * 如果你正在配置自己的 **负载均衡器**, 在多个可用区域中设置多台服务器用于 [双活](https://github.com/donnemartin/system-design-primer#active-active) 或 [主被](https://github.com/donnemartin/system-design-primer#active-passive) 将提高可用性
         * 终止在 **负载平衡器** 上的SSL，以减少后端服务器上的计算负载，并简化证书管理
     * 在多个可用区域中使用多台 **Web服务器**
-    * 在多个可用区域的 [**主-从 故障转移**](https://github.com/donnemartin/system-design-primer#master-slave-replication) 模式中使用多个 **MySQL** 实例来改进冗余
+    * 在多个可用区域的 [**主-从 故障转移**](https://github.com/donnemartin/system-design-primer#primary-replica-replication) 模式中使用多个 **MySQL** 实例来改进冗余
 * 分离 **Web 服务器** 和 [**应用服务器**](https://github.com/donnemartin/system-design-primer#application-layer)
     * 独立扩展和配置每一层
     * **Web 服务器** 可以作为 [**反向代理**](https://github.com/donnemartin/system-design-primer#reverse-proxy-web-server)
@@ -238,7 +238,7 @@
     * 来自 **Web 服务器** 的会话数据
         * **Web 服务器** 变成无状态的, 允许 **自动伸缩**
     * 从内存中读取 1 MB 内存需要大约 250 微秒，而从SSD中读取时间要长 4 倍，从磁盘读取的时间要长 80 倍。<sup><a href=https://github.com/donnemartin/system-design-primer#latency-numbers-every-programmer-should-know>1</a></sup>
-* 添加 [**MySQL 读取副本**](https://github.com/donnemartin/system-design-primer#master-slave-replication) 来减少写主线程的负载
+* 添加 [**MySQL 读取副本**](https://github.com/donnemartin/system-design-primer#primary-replica-replication) 来减少写主线程的负载
 * 添加更多 **Web 服务器** and **应用服务器** 来提高响应
 
 **折中方案, 可选方案, 和其他细节:**
@@ -344,7 +344,7 @@ SQL 扩展模型包括：
 
 ### SQL 扩展模式
 
-* [读取副本](https://github.com/donnemartin/system-design-primer#master-slave-replication)
+* [读取副本](https://github.com/donnemartin/system-design-primer#primary-replica-replication)
 * [集合](https://github.com/donnemartin/system-design-primer#federation)
 * [分区](https://github.com/donnemartin/system-design-primer#sharding)
 * [反规范化](https://github.com/donnemartin/system-design-primer#denormalization)

solutions/system_design/scaling_aws/README.md

@@ -207,7 +207,7 @@ Our **Benchmarks/Load Tests** and **Profiling** show that our single **Web Serve
         * If you are configuring your own **Load Balancer**, setting up multiple servers in [active-active](https://github.com/donnemartin/system-design-primer#active-active) or [active-passive](https://github.com/donnemartin/system-design-primer#active-passive) in multiple availability zones will improve availability
         * Terminate SSL on the **Load Balancer** to reduce computational load on backend servers and to simplify certificate administration
     * Use multiple **Web Servers** spread out over multiple availability zones
-    * Use multiple **MySQL** instances in [**Master-Slave Failover**](https://github.com/donnemartin/system-design-primer#master-slave-replication) mode across multiple availability zones to improve redundancy
+    * Use multiple **MySQL** instances in [**Primary-Replica Failover**](https://github.com/donnemartin/system-design-primer#primary-replica-replication) mode across multiple availability zones to improve redundancy
 * Separate out the **Web Servers** from the [**Application Servers**](https://github.com/donnemartin/system-design-primer#application-layer)
     * Scale and configure both layers independently
     * **Web Servers** can run as a [**Reverse Proxy**](https://github.com/donnemartin/system-design-primer#reverse-proxy-web-server)
@@ -238,7 +238,7 @@ Our **Benchmarks/Load Tests** and **Profiling** show that we are read-heavy (100
     * Session data from the **Web Servers**
         * The **Web Servers** become stateless, allowing for **Autoscaling**
     * Reading 1 MB sequentially from memory takes about 250 microseconds, while reading from SSD takes 4x and from disk takes 80x longer.<sup><a href=https://github.com/donnemartin/system-design-primer#latency-numbers-every-programmer-should-know>1</a></sup>
-* Add [**MySQL Read Replicas**](https://github.com/donnemartin/system-design-primer#master-slave-replication) to reduce load on the write master
+* Add [**MySQL Read Replicas**](https://github.com/donnemartin/system-design-primer#primary-replica-replication) to reduce load on the write master
 * Add more **Web Servers** and **Application Servers** to improve responsiveness
 
 *Trade-offs, alternatives, and additional details:*
@@ -313,7 +313,7 @@ We'll continue to address scaling issues due to the problem's constraints:
     * A data warehouse such as Redshift can comfortably handle the constraint of 1 TB of new content per month
 * With 40,000 average read requests per second, read traffic for popular content can be addressed by scaling the **Memory Cache**, which is also useful for handling the unevenly distributed traffic and traffic spikes
     * The **SQL Read Replicas** might have trouble handling the cache misses, we'll probably need to employ additional SQL scaling patterns
-* 400 average writes per second (with presumably significantly higher peaks) might be tough for a single **SQL Write Master-Slave**, also pointing to a need for additional scaling techniques
+* 400 average writes per second (with presumably significantly higher peaks) might be tough for a single **SQL Write Primary-Replica**, also pointing to a need for additional scaling techniques
 
 SQL scaling patterns include:
 
@@ -344,7 +344,7 @@ We can further separate out our [**Application Servers**](https://github.com/don
 
 ### SQL scaling patterns
 
-* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave-replication)
+* [Read replicas](https://github.com/donnemartin/system-design-primer#primary-replica-replication)
 * [Federation](https://github.com/donnemartin/system-design-primer#federation)
 * [Sharding](https://github.com/donnemartin/system-design-primer#sharding)
 * [Denormalization](https://github.com/donnemartin/system-design-primer#denormalization)