Sunday, January 13, 2013

Replicating from MySQL to Amazon RDS

There have been a number of comments that Amazon RDS does not allow users access to MySQL replication capabilities (for example here and here).  This is a pity. Replication is one of the great strengths of MySQL and the lack of it is a show-stopper for many users.  As of the latest build of Tungsten Replicator half of this problem is on the way to being solved. You can now set up real-time replication from an external MySQL master into an Amazon RDS instance.

In the remainder of this article I will explain how to set up Tungsten replication to an Amazon RDS slave, then add a few thoughts about why this feature is useful along with some suggestions for improvement.   To keep the article reasonably short I assume you understand the basics of installing Tungsten Replicator.  If you need more information, check out the online documentation.

Readying an RDS Test Instance

Amazon RDS is Amazon's on-demand relational database.  RDS supports several database types including MySQL, which I will use for this demonstration.  Launching a new instance is simple.  Login to the Amazon AWS Console using an account that has RDS enabled, then switch to the Amazon RDS Console.  Press the Launch a DB Instance button, whereupon a screen like the following appears:
RDS Database Selection
Press the Select button for MySQL Community Edition, which starts the configuration window.  (You can also replicate into Oracle if you are up for a challenge.  If you do this, please post what you did to get it to work!)  Next fill out properties for MySQL.
MySQL Instance Configuration
Among other things, you create a master login and password.  Note these carefully as you will need them to configure replication.  Then continue for another couple of screens, at which point you can launch your instance.  It takes about 10 minutes for new instances to spin up, after which you can see the instance properties in the AWS RDS Console.  Here's a screen shot of my test instance.
AWS RDS Console
Once the instance is up, test access.  This is of course necessary to prove the instance is running properly and that we can login from a remote location.  Note the host name in the Endpoint field.  This is a DNS entry for the new MySQL instance.  Using that and the master login, we can now fire up the mysql client from a remote host where we plan to run replication.

$ mysql -utungsten -p -htest.c4villnbpuq1.us-west-1.rds.amazonaws.com
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2125
Server version: 5.5.27-log Source distribution

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| innodb             |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.01 sec)

This looks quite good.  We are now ready to install and start replication.

Important note!  If you have trouble connecting you may need to tweak your Amazon security group settings to open up ports, especially if you are replicating from non-Amazon locations.  Amazon has a very cool feature that can guess your originating host IP and offer a CIDR address that covers the port range from which you are operating.  I used this when configuring my security groups.

Setting Up Tungsten Replication

It is possible to set up replication from a MySQL master directly to Amazon RDS using a single Tungsten Replicator process.  However, it is more versatile and simpler to set up two replicators:  one to read from the MySQL master, and another replicator to apply to the Amazon RDS slave.  I will therefore demonstrate this configuration.

We will assume you have a MySQL master already running and that it meets prerequisites for running Tungsten.  Let's now grab the Tungsten code and install a master replicator.  You can get fresh builds from the Tungsten Replicator builds page.

We will take a recent replicator build that contains the RDS changes, which are documented in Issue 425.  Use 2.0.7 build 177 or later. The main improvement is to add a non-privileged slave mode that avoids invoking any of the operations forbidden by Amazon.  Among other things Tungsten normally uses commands like 'SET SESSION SQL_LOG_BIN=0' to suppress writing to the binlog when it applies data on a slave.  This command requires SUPER privilege, hence causes problems for underprivileged RDS logins.

Unpack the code and install the master replicator in /opt/continuent.  This is no different from installing a normal Tungsten master.  My master host is logos1.  Here are sample commands to pull the code and set up the master.  The example shows the minimum options--if you have MySQL installed in a non-standard location or otherwise differ from a stock installation you may need to add additional options.

mkdir ~/staging
cd staging
wget --no-check-certificate https://s3.amazonaws.com/files.continuent.com/builds/nightly/tungsten-2.0-snapshots/tungsten-replicator-2.0.7-177.tar.gz
tar -xf tungsten-replicator-2.0.7-177.tar.gz
tungsten-replicator-2.0.7-177/tools/tungsten-installer \
  --master-slave  \
  --master-host=logos1 \
  --datasource-user=tungsten  \
  --datasource-password=your_passord  \
  --service-name=aws \
  --home-directory=/opt/continuent \
  --cluster-hosts=logos1 \
  --start-and-report

Next, set up the slave replicator.  For convenience I am going to install the slave on a separate host, named logos2, to avoid port clashes between the two replicators.  If you install on the same host, you'll need to install into another release directory location and use the --rmi-port and --thl-port options to avoid port overlaps.  Here is the command to set up the Amazon RDS slave.  Note that the tungsten-installer program can install code between hosts, which is an extremely useful feature.

tungsten-replicator-2.0.7-177/tools/tungsten-installer \
  --master-slave  \
  --cluster-hosts=logos2 \
  --master-host=logos1 \
  --datasource-host=test.c4villnbpuq1.us-west-1.rds.amazonaws.com \
  --datasource-user=tungsten  \
  --datasource-password=your_password  \
  --service-name=aws \
  --slave-privileged-updates=false \
  --home-directory=/opt/continuent \
  --skip-validation-check=InstallerMasterSlaveCheck \
  --skip-validation-check=MySQLPermissionsCheck \
  --start-and-report

You may see a few warnings during the RDS installation, as the tungsten-installer cannot verify some settings on the Amazon RDS host.  These can be ignored.  If everything goes well, you now have two replicators up and running.  You can check the status of the master and slave using the trepctl command, as in:

/opt/continuent/tungsten/tungsten-replicator/bin/trepctl -host logos1 status
/opt/continuent/tungsten/tungsten-replicator/bin/trepctl -host logos2 status

Both replicators should report that they are online.  Now complete the exercise by proving that replication works between the replicators.  We start by logging into the local MySQL instance, creating a new table in the test schema, and adding data.

$ mysql -uroot test
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 231488
Server version: 5.5.21-rel25.1-log Percona Server with XtraDB (GPL), Release rel25.1, Revision 234

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> create table foo(id int primary key);
Query OK, 0 rows affected (0.24 sec)

mysql> insert into foo values (256);
Query OK, 1 row affected (0.00 sec)

Now login to the Amazon RDS instance and look for table foo.  

$ mysql -utungsten -p -htest.c4villnbpuq1.us-west-1.rds.amazonaws.com test
Enter password: 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2161
Server version: 5.5.27-log Source distribution

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> select * from foo;
+-----+
| id  |
+-----+
| 256 |
+-----+
1 row in set (0.01 sec)

Mission accomplished!  We have real-time replication enabled from a MySQL master to Amazon RDS.  At this point you can replicate more or less normally.  There are some obvious limitations due to the fact that Amazon RDS is locked down and does not grant our login full privileges.  
  1. Temp table replication may not work.  Tungsten depends on being able to issue commands of the form "set @@session.pseudo_thread_id=23531" and the like.  This prevents clashes between temp tables of the same name on different master sessions.  You may need to enable row replication on the master, which suppresses temp table replication.  (For other approaches, see my previous article on temp tables and the binlog.) 
  2. Any command that requires SUPER privilege will not work.  As an obvious example, you will not be able to grant SUPER privilege to new accounts.  Such commands will break replication. 
  3. All replicated commands go into the binlog, which is a potential performance drag and may slow down Amazon RDS slaves.  Parallel replication may not help in this case, since committing to the binlog is a serialization point that blocks other transactions.  This problem may be cured if Amazon picks up group commit fixes from MySQL 5.6 and/or MariaDB.  
All things considered, however, these are minor inconveniences.  Most applications should be able to replicate without difficulties, especially if the master transaction rate is not too high.

Configuring SSL for Connections to RDS

In the previous demonstration I used a master host running outside Amazon.  This means my test transactions traveled across the Internet, where they were visible to all and sundry along the way.  To illustrate, we can run tcpdump and watch traffic as it goes by.

$ sudo tcpdump -A -vvv -s 256 host test.c4villnbpuq1.us-west-1.rds.amazonaws.com
...
logos2.46657 > ec2-54-241-56-140.us-west-1.compute.amazonaws.com.mysql: Flags [P.], cksum 0xb0f7 (incorrect -> 0x995d), seq 3012:3073, ack 3412, win 94, options [nop,nop,TS val 89630514 ecr 74223746], length 61
E..qw>@.@......n6.8..A..4..L...f...^.......
.W.2.l..9....insert into foo values (256) /* ___SERVICE___ = [aws] */
22:55:36.316049 IP (tos 0x8, ttl 51, id 26226, offset 0, flags [DF], proto TCP (6), length 63)

If we were handling confidential data, exposing traffic like this to possible evildoers would be a serious problem.  Fortunately, Amazon RDS supports SSL encrypted connections from clients.  Here is how to use it with Tungsten.

First, you need to get the Amazon RDS certificate, which is used to sign certificates for individual RDS instances.

mkdir /opt/continuent/certs
cd /opt/continuent/certs
wget https://rds.amazonaws.com/doc/mysql-ssl-ca-cert.pem

Next, you need to create a trust store that Java can access containing the certificates of signing authorities whom you trust.  For this you will need the Java keytool utility, which is included in the JDK.  If you are just using the Java runtime in production, you will need to generate the store on another host, then copy it over to your test hosts.  I used the password "secret" in this example.

$ keytool -import -alias rds -file mysql-ssl-ca-cert.pem -keystore truststore
Enter keystore password:  
Re-enter new password: 
Owner: CN=aws.amazon.com/rds/, OU=RDS, O=Amazon.com, L=Seattle, ST=Washington, C=US
Issuer: CN=aws.amazon.com/rds/, OU=RDS, O=Amazon.com, L=Seattle, ST=Washington, C=US
...
Trust this certificate? [no]:  yes
Certificate was added to keystore

We now need to tell the slave replicator about the truststore file using Java VM options.  On the slave host, edit /opt/continuent/tungsten/tungsten-replicator/conf/wrapper.conf and add the extra options shown in bold face.  

# Java Additional Parameters
wrapper.java.additional.1=-Dreplicator.home.dir=../../tungsten-replicator/
wrapper.java.additional.2=-Dreplicator.log.dir=../../tungsten-replicator/log
wrapper.java.additional.3=-Dcom.sun.management.jmxremote
wrapper.java.additional.4=-Djavax.net.ssl.trustStore=/opt/continuent/certs/truststore
wrapper.java.additional.5=-Djavax.net.ssl.trustStorePassword=secret

The last step is to enable SSL encryption when applying data.  We need to set an extra URL option on the drizzle JDBC driver to turn on SSL. For this we need to edit the static-svc.properties file that configures replication.  In my example this file is located in /opt/continuent/tungsten/tungsten-replicator/conf/static-aws.properties.  Open the file and look for the section that starts with APPLIERS. Edit the text to add additional urlOptions line as shown below.  

############
# APPLIERS #
############

replicator.applier.dbms=com.continuent.tungsten.replicator.applier.MySQLDrizzleApplier
replicator.applier.dbms.host=${replicator.global.db.host}
replicator.applier.dbms.port=${replicator.global.db.port}
replicator.applier.dbms.user=${replicator.global.db.user}
replicator.applier.dbms.password=${replicator.global.db.password}
replicator.applier.dbms.urlOptions=?useSSL=true
replicator.applier.dbms.ignoreSessionVars=autocommit
replicator.applier.dbms.getColumnMetadataFromDB=true

Restart the replicator process (/opt/continuent/tungsten/tungsten-replicator/bin/replicator restart) and you will now be using SSL encryption.  If we now look back at the tcpdump outout, it looks like garbage as the following example shows. 

...
23:46:52.370904 IP (tos 0x0, ttl 64, id 5899, offset 0, flags [DF], proto TCP (6), length 105)
    logos2.44717 > ec2-54-241-56-140.us-west-1.compute.amazonaws.com.mysql: Flags [P.], cksum 0xb0ef (incorrect -> 0xd834), seq 3087:3140, ack 4838, win 102, options [nop,nop,TS val 89938121 ecr 74992771], length 53
E..i..@.@.r....n6.8......zSR.b.....f.......
.\X..xL.....07..|..x.)...T..888.H/...iz...^.W8....'...... ..J
...

This is much better.  We are replicating to an Amazon RDS, and the transactions are safe from prying eyes.  If you have gotten this far you are ready to try your own applications.  

Benefits of Replication into Amazon RDS

Amazon RDS is convenient thanks to its quick and simple setup, but the lack of replication is a severe limitation in building systems that need more than a single MySQL instance.  In particular it makes it hard to integrate RDS into systems that consist of more than Amazon RDS itself.  Adding the ability to replicate in real-time into RDS therefore has a number of benefits.  The most obvious include using RDS to extend existing systems.

First, Amazon RDS can offer a quick way to add read capacity to existing MySQL applications.  This is especially useful if you have a cluster, such as Tungsten, which handles your transaction processing and overall HA.  You can now add Amazon RDS read slaves that you discard when no longer needed.  Tungsten Replicator has a number of other useful features like the ability to read from a group of nodes, not just one, that make such topologies easy to set up and maintain.  Clusters other than Tungsten will likewise benefit from this feature. 

Second, Amazon RDS is suitable for applications that do not need 24x7 high availability (limitations include slow failover, no online maintenance, no cross-cloud capabilities, etc.)  You can now pull data from other sources and send them to Amazon RDS slaves for processing, which amounts to extending overall processing capacity.  For example, you could use RDS to run back-office tasks using transactions replicated in from MySQL masters.  Tungsten Replicator also replicates data from Oracle, so this is an additional source of transactions.  

There are of course other ways to replicate data to and from RDS, for example using batch ETL tools like Talend.  However, these are not real-time and often require application changes to add timestamp columns or otherwise mark transactions that need to be extracted.  Log-based replication as implemented by Tungsten is fast and has minimal impact on applications or MySQL itself.  

Thoughts about Further Improvements for Amazon RDS Replication

On our side, i.e., at Continuent, we need to do more testing, add documentation, and fix problems as they arise.  We are starting a beta test with one of our customers in the next few days, who incidentally was the same customer who requested this feature in the first place after hacking it for themselves.  RDS also has some interesting provisioning capabilities that I would like to understand better.  We are also adding options that eliminate the need for manual configuration of security settings.  This will keep us busy for a while.

Other improvements depend on changes to RDS itself.  An obvious and huge improvement would be to permit replication out of Amazon RDS.  Unfortunately, Tungsten needs a login that has REPLICATION_SLAVE privilege so that we can download binlog data.  That privilege is not yet available to Amazon users.  Once it is, Tungsten extraction will also work in very short order. We actually don't need other commands like START/STOP SLAVE or FLUSH LOGS--just ability to issue a COM_BINLOG_EVENT from a client connection and receive binlog records.  I am sure other products would use this capability as well.  (RDS developers, if you are listening here's an easy way to extend your product usability significantly...)

Replication is such a valuable feature of MySQL that Amazon RDS feels somewhat crippled without it.  For this reason I would imagine that Amazon will open up additional capabilities in the future.  Until then we will polish up replication from MySQL masters to Amazon RDS slaves, awaiting a time when we can add more features.  

In the meantime, I hope you will try the new replication to Amazon RDS.  As noted in this article you can grab the latest builds and try it yourself.  Please report your experiences through either Continuent Support if you are a customer or the Tungsten discussion list if you use the open source Tungsten Replicator.  I look forward to your feedback and suggestions for making Amazon RDS support better. 

19 comments:

hingo said...

TL;DR... but the headline is all I wanted to know. Once again Tungsten goes where no man/replication solution has gone before.

Now, can you also replicate out of RDS? (Assume that some time in the future they will support the binlog client api thing, does that help?) RDS is a terrible lock-in scheme from which you can't migrate away without downtime. Tungsten could solve that. Of course, for now, you probably have more demand for this solution that takes people onto RDS in the first place :-)

henrik

Robert Hodges said...

Heh, thanks Henrik!

If RDS would allow us to use the binlog API I could get extraction working in a few hours. We currently make the odd call to FLUSH LOG which would need to be suppressed. Beyond that it should work fine, as RDS is just MySQL 5.5.27 under the covers. If there are functional differences I have not seen them yet.

Justin Swanhart said...

This only works with STATEMENT based replication, right?

Replicating row based would require running the BINLOG statement which requires SUPER privs, or am I wrong?

Henrik:
Unfortunately, without access to the binary logs (either through a normal replication user granted REPLICATION SLAVE and REPLICATION CLIENT, or via direct disk access to binlogs) I don't think it will ever be possible to replicate out of RDS. Right now that the only migration path out of RDS is mysqldump and that likely won't change soon.

Justin Swanhart said...

Nice work though, even if it is only statement that is a good step forward.

Robert Hodges said...

@Justin, you can replicate either rows or statements from MySQL masters. Tungsten handles both. Row changes turn into prepared SQL on the slave end.

As far as replicating out, I would not be so sure this is impossible. It requires a hack to MySQL to separate the privilege to download binlogs from manipulating the slave. Over time I it will be attractive to do this, I think.

hingo said...

At least for me the main argument against running anything serious in RDS is the lock-in you get into: no way to migrate away from it without downtime.

Still, like I said, Tungsten here has solved the opposite problem: at least you can now migrate into RDS without downtime! Worry about your future problems some other day ;-)

Cloud Hosting said...
This comment has been removed by the author.
Vineet Khanna said...

First of all thanks for great implementation.

=>you can replicate either rows or statements from MySQL masters. Tungsten handles both. Row changes turn into prepared SQL on the slave end.

So can we use mixed mode replication or we have to choose only one from rows & statements.

Vincent Jørgensen said...

I've almost got this working. Right now, on the W replicator (logos2 in your tutorial). But when I go to start it, I get this error:
13:26 Fri Jun 28 $ /opt/tungsten-replicator/tools/tungsten-installer-2.1.1-25 \
> --master-slave \
> --cluster-hosts=10.11.0.59 \
> --master-host=10.11.0.235 \
> --datasource-host=rdsdb.cfwimw2efneb.us-east-1.rds.amazonaws.com \
> --datasource-user=root \
> --datasource-password=*** \
> --service-name=aws \
> --slave-privileged-updates=false \
> --home-directory=/opt/continuent \
> --skip-validation-check=InstallerMasterSlaveCheck \
> --skip-validation-check=MySQLPermissionsCheck \
> --start-and-report
ERROR >> 10.11.0.59 >> Binary logs are not enabled on root@rdsdb.cfwimw2efneb.us-east-1.rds.amazonaws.com:3306 (WITH PASSWORD)
WARN >> 10.11.0.59 >> Unable to check the MySQL config file '/etc/my.cnf'
WARN >> 10.11.0.59 >> Unable to compare the configured server-id to the one in '/etc/my.cnf'
WARN >> 10.11.0.59 >> Unable to compare the configured port to the one in '/etc/my.cnf'
WARN >> 10.11.0.59 >> The value of max_allowed_packet is too small for root@rdsdb.cfwimw2efneb.us-east-1.rds.amazonaws.com:3306 (WITH PASSWORD)
#####################################################################
# Validation failed
#####################################################################
#####################################################################
# Errors for 10.11.0.59
#####################################################################
ERROR >> 10.11.0.59 >> Binary logs are not enabled on root@rdsdb.cfwimw2efneb.us-east-1.rds.amazonaws.com:3306 (WITH PASSWORD) (MySQLBinaryLogsEnabledCheck)
Check that the MySQL user can run "show variables like 'log_bin'"
Add "log-bin=mysql-bin" to the MySQL configuration file.
---------------------------------------------------------------------

The only things I'm doing differently are 1) Using MySQL 5.1, 2) Using W 2.1.1-25, and and 3) running inside a VPC. Are either of those things causing this error?

Robert Hodges said...

@Vincent,

Try adding --skip-validation= MySQLBinaryLogsEnabledCheck and see if it gets you past the problem. I would also post on the replicator discussion group if you have further problems. We check those lists pretty regularly. (URL: https://groups.google.com/forum/#!forum/tungsten-replicator-discuss)

Robert Hodges said...

(Oops, that is --skip-validation-check= MySQLBinaryLogsEnabledCheck)

程兵 said...

Hi, Robert Hodges:
It seems that Tungsten cannot set RDS as a master, right?
Is there a good solution to replicate out of RDS? Hope for your answer, thanks.

Robert Hodges said...

@程兵, unfortunately that's correct. The reason is that Amazon RDS does not grant clients the REPLICATION SLAVE privilege or at least did not at the time of writing this article. If it did, we could replicate out of an RDS master by logging in and downloading the binlog contents, which we would then replicate using Tungsten's own logs. Tungsten supports this using the --disable-relay-logs option.

fermion said...

This is now possible:

http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Procedural.Importing.NonRDSRepl.html?ref_=pe_395030_32399930

Robert Hodges said...

@fermion, that's an interesting development and caught my attention as well. It does not solve the main problem, which is replicating *out* of RDS. However, it's reasonable to suppose Amazon may have something on the way for that as well.

Ivan Korjavin said...

Looks like a pain

Robert Hodges said...

@Ivan, it's really not that difficult if you try it. You are also welcome to suggest a better way.

Asish Kumar Samanta said...

I have tow mysql instances in two different EC2 in AWS and I have one RDS.

I want mysql instances in two different EC2 will be master and MYSQL instances in RDS will be slave.

How to install tungsten replicator (FAN-IN topology) for the above mentioned purpose.

Robert Hodges said...

Hi Ashish,

This question should be posted on the replication discussion group, which I believe you already did.(https://groups.google.com/forum/#!forum/tungsten-replicator-discuss)

Cheers, Robert

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