Some of the key things to think about when putting your application on the cloud are discussed below. Cloud computing is relatively new, and best practice is still being established. However we can learn from earlier technologies and concepts such as utility compute, SaaS, outsourcing and even internal enterprise centre management, as well as from experience with vendors such as Amazon and FlexiScale.

Licensing: If you are using the cloud for spikes or overspill make sure that the products you want to use in the cloud can be used in this way. Certain products restrict their licenses to be used from a cloud perspective. This is especially true of commercial Grid, HPC or DataGrid vendors.

Data transfer costs: When using a provider like Amazon with a detailed cost model, make sure that any data transfers are internal to the provider network rather than external. In the case of Amazon, internal traffic is free but you will be charged for any traffic over the external IP addresses.

Latency: If you have low latency requirements then the Cloud may not be the best environment to achieve this. If you are trying to run an ERP or some such system in the cloud then the latency may be good enough but if you are trying to run a binary or FX Exchange then of course the latency requirements are very different and more stringent. It is essential to make sure you understand the performance requirements of your application and have a clear understanding of what is deemed business critical.

One vendor who has focused on attacking low latency in the cloud is GigaSpaces and so if you require cloud low latency then these are one of the companies you should evaluate. Also for processing distributed data loads there is the map reduce pattern and Hadoop. These type of architectures eliminating the boundaries created by scale-out database based approaches.

State: Check whether your cloud infrastructure providers have persistence. When an application is brought down and then back up all local changes will be wiped and you start with a blank slate. This obviously has ramifications with instances that need to store user or application state. To combat this on their platform Amazon delivered EC2 persistent storage in which data can remain linked to a specific computing instance. You should ensure you understand the state limitations of any Cloud Computing platform that you work with.

Data Regulations: If you are storing data in the cloud you may be breaching data laws depending where your data is stored i.e. which country or continent. To combat this Amazon S3 now supports location constraints, which allow you to specify where in the world to store data for a bucket and provides a new API to retrieve the location constraint for an existing bucket. However if you are using another cloud provider you should check where your data is stored.

Dependencies: Be aware of dependencies of service providers. If service ‘y’ is dependant on ‘x’ then if you subscribe to service ‘y’ and service ‘x’ goes down you lose your service. Always check any dependencies when you are using a cloud service.

Standardisation: A major issue with current cloud computing platforms is that there is no standardisation of the APIs and platform technologies that underpin the services provided. Although this represents a lack of maturity you need to consider how locked in you are when considering a Cloud platform or migrating between cloud computing platforms will be very difficult if not impossible. This may not be an issue if your supplier is IBM and always likely to be IBM, but it will be an issue if you are just dipping your toe in the water and discover that other platforms are better suited to your needs.

Security: Lack of security or apparent lack of security is one of the perceived major drawbacks of working with Cloud platform and Cloud technology. When moving sensitive data about or storing it in public cloud it should be encrypted. And it is important to consider a secure ID mechanism for authentication and authorisation for services. As with normal enterprise infrastructures only open the ports needed and consider installing a host based intrusion detection systems such as OSSEC. The advantage of working with an enterprise Cloud provider, such as IBM or Sun is that many of these security optimisations are already taken care of. See our prior blog entry for securing n-tier and distributed applications on the cloud. Be sure to check out Amazon’s new VPC inititative as well as looking at VPN-Cubed by CohesiveFT if you have to tie together public Clouds with private applications, services or infrastructure. If you need to keep costs down and evaluate free then look at OpenVPN.

Compliance: Regulatory controls mean that certain applications may not be able to deployed in the Cloud. For example the US Patriot Act could have very serious consequences for non-US firms considering U.S. hosted cloud providers. Be aware that often cloud computing platforms are made up of components from a variety of vendors who may themselves provide computing in a variety of legal jurisdictions. Be very aware of the dependencies and ensure you factor this into any operational risk management assessment. See also my prior blog entry on this topic

Quality of service: You will need to ensure that the behaviour and effectiveness of the cloud application that you implement can be measured and tracked both to meet existing or new Service Level agreements. We have discussed previously some of the tools that come with this option built in (GigaSpaces) and other tools that provide functionality that enable you to use this with your Cloud Architecture (RightScale, Scalr etc). Achieving Quality of Service will encompass scaling, reliability, service fluidity, monitoring, management and system performance.

System hardening: Like all enterprise application infrastructures you need to harden the system so that it is secure, robust, and achieves the necessary functional requirements that you need. See my prior blog entry on system hardening for Amazon EC2.