Merge pull request #2 from donnemartin/master

 Update Cassandra architecture links (donnemartin#213)

README.md

@@ -23,7 +23,7 @@ This repo is an **organized collection** of resources to help you learn how to b
 
 ### Learn from the open source community
 
-This is an early draft of a continually updated, open source project.
+This is a continually updated, open source project.
 
 [Contributions](#contributing) are welcome!
 
@@ -997,7 +997,7 @@ Document stores provide high flexibility and are often used for working with occ
 
 A wide column store's basic unit of data is a column (name/value pair).  A column can be grouped in column families (analogous to a SQL table).  Super column families further group column families.  You can access each column independently with a row key, and columns with the same row key form a row.  Each value contains a timestamp for versioning and for conflict resolution.
 
-Google introduced [Bigtable](http://www.read.seas.harvard.edu/~kohler/class/cs239-w08/chang06bigtable.pdf) as the first wide column store, which influenced the open-source [HBase](https://www.mapr.com/blog/in-depth-look-hbase-architecture) often-used in the Hadoop ecosystem, and [Cassandra](http://docs.datastax.com/en/archived/cassandra/2.0/cassandra/architecture/architectureIntro_c.html) from Facebook.  Stores such as BigTable, HBase, and Cassandra maintain keys in lexicographic order, allowing efficient retrieval of selective key ranges.
+Google introduced [Bigtable](http://www.read.seas.harvard.edu/~kohler/class/cs239-w08/chang06bigtable.pdf) as the first wide column store, which influenced the open-source [HBase](https://www.mapr.com/blog/in-depth-look-hbase-architecture) often-used in the Hadoop ecosystem, and [Cassandra](http://docs.datastax.com/en/cassandra/3.0/cassandra/architecture/archIntro.html) from Facebook.  Stores such as BigTable, HBase, and Cassandra maintain keys in lexicographic order, allowing efficient retrieval of selective key ranges.
 
 Wide column stores offer high availability and high scalability.  They are often used for very large data sets.
 
@@ -1006,7 +1006,7 @@ Wide column stores offer high availability and high scalability.  They are often
 * [SQL & NoSQL, a brief history](http://blog.grio.com/2015/11/sql-nosql-a-brief-history.html)
 * [Bigtable architecture](http://www.read.seas.harvard.edu/~kohler/class/cs239-w08/chang06bigtable.pdf)
 * [HBase architecture](https://www.mapr.com/blog/in-depth-look-hbase-architecture)
-* [Cassandra architecture](http://docs.datastax.com/en/archived/cassandra/2.0/cassandra/architecture/architectureIntro_c.html)
+* [Cassandra architecture](http://docs.datastax.com/en/cassandra/3.0/cassandra/architecture/archIntro.html)
 
 #### Graph database
 
@@ -1289,11 +1289,11 @@ Message queues receive, hold, and deliver messages.  If an operation is too slow
 
 The user is not blocked and the job is processed in the background.  During this time, the client might optionally do a small amount of processing to make it seem like the task has completed.  For example, if posting a tweet, the tweet could be instantly posted to your timeline, but it could take some time before your tweet is actually delivered to all of your followers.
 
-**Redis** is useful as a simple message broker but messages can be lost.
+**[Redis](https://redis.io/)** is useful as a simple message broker but messages can be lost.
 
-**RabbitMQ** is popular but requires you to adapt to the 'AMQP' protocol and manage your own nodes.
+**[RabbitMQ](https://www.rabbitmq.com/)** is popular but requires you to adapt to the 'AMQP' protocol and manage your own nodes.
 
-**Amazon SQS**, is hosted but can have high latency and has the possibility of messages being delivered twice.
+**[Amazon SQS](https://aws.amazon.com/sqs/)** is hosted but can have high latency and has the possibility of messages being delivered twice.
 
 ### Task queues
 

solutions/system_design/mint/README.md

@@ -136,7 +136,7 @@ Data flow:
 
 * The **Client** sends a request to the **Web Server**
 * The **Web Server** forwards the request to the **Accounts API** server
-* The **Accounts API** server places a job on a **Queue** such as Amazon SQS or [RabbitMQ](https://www.rabbitmq.com/)
+* The **Accounts API** server places a job on a **Queue** such as [Amazon SQS](https://aws.amazon.com/sqs/) or [RabbitMQ](https://www.rabbitmq.com/)
     * Extracting transactions could take awhile, we'd probably want to do this [asynchronously with a queue](https://github.com/donnemartin/system-design-primer#asynchronism), although this introduces additional complexity
 * The **Transaction Extraction Service** does the following:
     * Pulls from the **Queue** and extracts transactions for the given account from the financial institution, storing the results as raw log files in the **Object Store**