Is there a benefit for using prebuilt connectors to and from SaaS billing platforms like Aria/Zuora when they live between Salesforce and Netsuite used as pure CRM and ERP/Acounting/Finance respectively. That is, versus using an ESB/Integration platform like Mulesoft or Boomi.
We are currently looking at changing billing and ERP systems and having them integrate together and with Salesforce CRM. So the chain would look like:
CRM -- Billing Solution -- ERP
Many of the billing systems have prebuilt connectors that work with ERP systems like Netsuite or Fusion, as well as connectors for Salesforce. Not to mention web service end points/APIs.
But there are integration vendors like Mulesoft and Boomi (basically Enterprise Service Bus PaaS providers) that also allow integration between the services.
I come from a SOA background and tend to favour a standalone ESB to connect the systems but due to my lack of familiarity with Saas ERP systems don't understand the benefits and pitfalls in the prebuilt connector vs ESB debate. I understand the concepts behind avoiding point to point integration, which would turn around to being a benefit for using ESBs. But is there a benefit for using prebuilt connectors within the SaaS platforms ... and are there serious downsides (my main concern).
Can anyone provide some insight here? I am not asking for "which one is best", just some real world experience good or bad that could help someone make these kinds of decisions.
I cannot provide a comprehensive comparison between the services you plan on using, but your question is quite interesting so I thought I'd share my thoughts and experience and hope you'll benefit from it.
Prebuilt connectors are not something new - they existed long before SaaS and iPaaS became a thing. So their pros and cons are still the same, the main issues you will be looking at are still very much related to the lack of flexibility you'll be facing and of course, the shortcomings of point-to-point integration. Things are somewhat refracted via the prism of SaaS/iPaaS but I believe that most aspects are still relevant.
Prebuilt Connector capabilities and support
You need to assess to what extent a prebuilt connector really covers the integration between the two systems. Services like salesforce take pride in their customizability and extensibility by using 3rd party extensions. In most cases the connector will be following a one-size-fits-all approach that only satisfies the most common and simple of all integration needs. It's all fun and games until something has to change. It is not possible to know in advance what you could need the future but think about it - would you be able to count on having your customisations and extensions covered by the prebuilt connector in case you decide to integrate them as well?
Another point you must consider is support - what happens if one of those companies decide to suddenly announce that they will stop supporting future integration via prebuilt connectors you are already using? You should check to see if there are any guarantees for you.
Tight Coupling and Service provider lock-in
Using point to point connectors will couple systems to each other so you’ll be severely limiting your options to switch between platforms if you need to at some point. It might seem a fairly simple integration scenario now, but adding more systems to the mix over time generally makes things even worse, since you are going to have dependencies here and there, and not every new system will have a connector out of the box to integrate easily with all the others you're already using. Having a middleware gives you the precious ability to map and transform data if needed, and maybe even apply some business logic that makes your life much easier (and cheaper). Also you'd be able to replace a system without having to replace others depending on it.
Consider your scenario: if you decide to change the billing system, you will have to find one that’s being properly supported by both the CRM and ERP providers. Thus, you could potentially remain locked into using exactly these three, even though for example they don’t fit your needs anymore or there is something else on the market that would have given you great competitive advantage if only you could integrate with it.
Orchestration and future investments
An important note about the p-2-p scenario is that you will not be able to implement process services that span across all the systems if needed. The added flexibility and benefits of using even simple forms of orchestration (I’m not even talking about achieving what can be achieved with a full featured business process management) will be off reach for your business. When the market changes and Time to Market is the deciding factor you may be not be prepared.
Thoughts on choosing iPaaS
Using iPaaS platform looks like a much better decision in the long run. Yet, you still have to make sure that the platform does not just give you some set of predefined connectors and drag&drop beauties (they all do), but also the ability to easily implement your very own integrations from scratch while supporting industry standards. I think that it is absolutely crucial to have this kind of flexibility when talking about an ESB solution, be it in the cloud or on premises.
The potential cons of the iPaaS approach would be:
you come to depend on yet another service provider and you will have more costs because the service is not free;
your data travels to another service provider, so there is additional risk in terms of security, no matter what the service providers may try to tell you;
more upfront effort spent on design and implementation;
additional burden, related to having to maintain integration and accommodate potential changes (however rare they might be) if a new version comes out.
Conclusion
It’s all really a tradeoff between desired flexibility and the investment that you’re willing to make. Your decision will heavily depend on the current state of your business and your growth expectations going forward, rather than the purely technical side of things.
I hope my thoughts gave your some perspective. Please update the question with your decision and reasoning when the time comes. Good luck!
Related
We've narrowed our selection for an ipaas down to the above 3.
Initially we're looking to pass data from a cloud based HR system to Netsuite, and from Netsuite to Salesforce, and sometimes JIRA.
i've come from a Mulesoft background which I think would be too complex for this. On the other hand it seems that Celigo is VERY drag and drop, and there's not much room for modification/customisation.
Of the three, do you have any experience/recommendations? We aren't looking for any code heavy custom APIs, most will just be simple scheduled data transfers but there may be some complexity within the field mapping, and we want to set ourselves up for the future.
I spent a few years removing Celigo from NetSuite and Salesforce. The best way I can describe Celigo is that it is like the old school anti-virus programs which were often worse than the viruses... lol... It digs itself into the end system, making removing it a nightmare.
Boomi does the job, but is very counter-intuitive, and overly complex. You can't do everything from one screen, you can't easily bounce back and forth between tasks/operations/etc. And, sometimes it is very difficult to find where endpoints are used, as they are not always shown in their "where is this used" feature. Boomi has a ton of endpoint connectors pre-built (the most, I believe), but I have not seen an easy way to just create your own. Boomi also has much more functionality than just the integrations, if that is something that may be needed.
Jitterbit, my favorite, is ridiculously simple to use. You can access everything from one main screen, you can connect to anything (as long as it can reach out to the network, or you can reach it via the network - internal or external). Jitterbit has a lot of pre-built endpoint connectors. It is also extremely easy to just create a connection to anything you want. The win with Jitterbit is that it is super easy to use, super easy to learn, it always works, they have amazing support (if you need it). I have worked with Jitterbit the most (about 6 years), and I have never been unable to complete an integration task in less that a couple of day, max.
I have extensive experience with Dell Boomi platform but none with JitterBit or Celigo. Dell Boomi offers very versatile and well supported iPaaS solution. The technical challenges of Boomi are some UI\usability issues (#W3BGUY mentioned the main ones) and the lack of out-of-the-box support for CI/CD and DevOps processes (code management, versioning, deployments etc.)
One more important component to consider here is the pricing of the platform. Boomi does charge their clients yearly connection prices. Connection is defined as a unique combination of URL, username and password. The yearly license costs vary and can range anywhere between ($1,000 - $12,000) per license per year. The price depends greatly on your integration landscape and the discounts provided so I would advise on engaging with vendor early to understand your costs. Would be great to hear from others on pricing for JitterBit and Celigo.
Boomi is also more than just an iPaaS platform. They offer other modules of their platform to customers: API Management, Boomi Flow (workflow and automation module), Master Data Hub (master data management). Some of these modules are well developed and some are in their infancy (API Management).
From my limited experience with MuleSoft platform, I share the OP's sentiments about it being too complex for simple integrations. They do provide great CI/CD and DevOps functionality though if that is something that is needed.
There is not a simple answer to a question like this. One needs to look at multiple aspects of the platform and make a decision based on multitude of factors. I would advise looking at Gartner and Forrester reports for a general guidelines and working out the pricing (initial and recurring) with the vendor.
I have only used Jitterbit, so can only comment on that. It works fine. It is pretty intuitive and easy to use, but does have some flexibility with writing your own queries, defining and mapping file formats, and choosing different transfer protocols.
I've only used the free version (which you need to host somewhere and also is not supported) and it was good enough for production tasks. If you have the luxury of time, I'd say download it and try it out. If it works for you, throw it on a server or upgrade to the cloud version.
One note: Jitterbit uses background services. If you run it locally and then decide to migrate your account to a server, you need to stop those services on your local. Otherwise, it will try to run jobs from both locations and that doesn't turn out well.
Consider checking out Choreo as well. It has a novel simultaneous code + low-code approach for integration development. And provides rich AI support for performance monitoring, debugging, and data mapping.
Disclaimer: I'm a member of the project.
Scenario :
I am having an application where I am using AWS Lambdas which are written in Kotlin to query data from a relational DB residing in AWS.
--
My problem is that I want to use an ORM for firing these queries. I dont want to use hibernate as it is too heavy and takes too long to setup, and I need a solution that would take up the least time in setting up and firing from the Lambdas. I have looked upon multiple ORMSs like Exposed, Requery, Jooq, Ktorm and Squash.
Is anybody out there having experience with any of these libraries in the serverless context? What are your experiences with them and what would you suggest using in my scenario?
You can have a look at exposed, https://github.com/JetBrains/Exposed
I have been using Squash with the Hikari connection pool for some large projects and I have been very happy with it. I like that is is very extensible and my team has been able to solve any issues that come up, implementing extensions to the dialect and the simplicity of defining TableDefinition classes makes it work well for generating code. It is also very self contained with very few dependencies and light on reflection, so should be good for serverless though I have not personally used it for that.
Squash is less an ORM than an sql abstraction / translation layer that ties into entities and it doesn't try to solve all the problems that something like hibernate does. In my experience ORMs start as simple, efficient, and powerful projects and grow to heavyweight libraries that try to do too much and their complexity begins to cause issues when the developer cannot easily see what's going on in the chain from usage through to the database / storage mechanism.
One negative about squash that deserves mention is that, while it is a jetlbrains official library and created by a kotlin developer, support is limited as orangy, the creator, is quite busy and I have feature pull requests outstanding, with many more of them backed up currently. I chose it because I favored it's simplicity and extensibility among a small but advanced team of developers all capable of improving upon it.
Which ever library you choose I hope these factors assist you in making your decision at the least.
I was trying to get a fix on when using Apache Camel would be appropriate and inappropriate from reading this article -- https://dzone.com/articles/when-use-apache-camel . What the article mentions is that when the number of services is low, using an integration framework like Camel might be overkill, which makes sense. But I was confused by this sentence
Although FuseSource offers commercial support, I would not use Apache
Camel for very large integration projects. An ESB is the right tool
for this job in most cases. It offers many additional features such as
BPM or BAM. Of course, you could also use several single frameworks or
products and „create“ your own ESB, but this is a waste of time and
money (in my opinion).
Is this because the integration framework lacks components that an ESB provides? If so, what are those?
At a functional level, Apache Camel does everything that all the other ESB's do and is a fine choice for pretty much any integration work. It has connectors (components in camel-speak) for every transport you can think of, deals with clustering, can provide a JMS broker and whatever else you need to integrate.
It doesn't have the nice UI's and IDEs that other tools (Tibco, webMethods, Boomi etc) which is a big advantage. The developers might actually write unit tests if you use Camel :) I'm joking of course, integration devs never write unit tests.
In terms of "weight" Camel itself is not too bloated. It can be used as a standalone runtime or you can simply leverage the integration capabilities as a library in another app. It heavily utilises spring and can run a large number of threads, so requires a reasonable amount of memory (~512Mb JVM Heap would be the lower bound) but is not difficult to use. It wont fight you.
JBoss Fuse is the full blown Red Hat supported Enterprise ESB. It is based around Camel, but uses apache karaf as the runtime which is a OSGi container. This is heavy weight but gives you a very powerful ESB runtime, deployment model and management interface and you can buy commercial support for Fuse and ActiveMQ from Red Hat. This is the more traditional "ESB" platform, but deep down inside all the integration functionality comes from Camel.
I have been working with various products that are used to implement ESBs in the past 10 years: Apache Camel, Mule, Oracle Service Bus, IBM Integration Bus (WebSphere Message Broker), Spring Integration, FUSE, etc. I can tell you what are the differences from various perspectives, but most importantly, what you have to understand is that ESB is an abstract concept - basically a "bus" in terms of integration patterns that connects various services in an entreprise. For this reason, you can build an ESB with a product that targets this specific need (e.g. IIB) or you can build it with something much more generic (e.g. SpringIntegration).
Management point of view:
The top-end commercial products (the ones you refer to "ESBs") like the ones from Oracle or IBM are well suited for this job. They have nice user interfaces that are made for implementing a bus pattern. On the workforce market you will need to find (may be simple or not) certified specialists to operate these products. Behind these products you will get support of big companies with which the enterprise may already have existing contracts. Often these products will have very specific connectors that may (or not, see developer point of view) ease your life. To give you an example, IBM's product will have very efficient connectors for IBM MQ or Mainframe CICS. They also offer out-of-the box integrations with other products like BPM. When building bigger implementations of ESBs, the projects are structured by the fact that not everything can be done in such a product - this means that you have smaller risk but also less flexibility. In terms of problems management, you are relatively safe because you blame the big company that supports you.
Towards the more "open" products/frameworks like FUSE, Mule, Camel, etc., you will start getting very flexible software that may be also cheaper as a start price. For working with it you will need generic profiles, but you will also need software architects to design your product because nothing forces you build the message flows in a particular way. At a certain point you will need at least some very skilled developers because you may not get efficient support, depending on the product you choose. In terms of problems management, you are fully responsible for this choice.
Developer point of view:
Top-end commercial products will come with in-built connectors and other operators - quick to build a POC. However, any customization will be a pain (for instance you may have an HTTP connector, but you may need to switch to some new SHA algorithm that has not been standard at the time you installed). The introduction of specific custom connectors will be possible, but much more complicated than with "open" products. You'll get nice user interfaces that will hide the code. This will mean a series of drawbacks for you, for instance code repository usage will not be efficient (can't diff two versions), unit tests are difficult to write, etc. The integrations with other products like BPM will force you to use a pre-chosen product, anything else will be doable but expensive.
The open-end products/frameworks will be flexible, everybody in the team will understand the product quickly (e.g. provided everyone knows Spring). Changing some core functionality might be very cheap. However, things can quickly degenerate if there is no supervision of experienced members because you can code pretty much anythig.
Architect point of view:
That said, there is something about the ESB that you should know in advance. You should be very clear in terms of capabilities of what you need to do (let's say: routing, service discovery, protocol conversion, etc.). Should you need to implement something complex in an ESB, for instance transformation of the business message, means that the business analyst will need to interact with your ESB. So for instance the expert in banking payments will need to write an XSLT for you. This XSLT might be simple, but it may also cause big trouble, for which you will be responsible. Now if this person also needs to know the product of your choice, this complicates things. Therefore the added value of integrating an ESB with BPM, BAM, etc. is very questionable.
Another thing to note is that for most enterprises nowadays, the ESB is not something that would create some competitive advantage, like for instance a web page. So investing in a super complex development or out-of-the-box product needs to be challenged.
Conclusion
Not sure if it was overwhelming or understandable, but in the end it boils down to the resources you have and the complexity of the task.
Just as a comment, contrary to another answer on this question, if you are building something complex:
Pay attention to the Architect's point of view above.
You may seriously consider the open end of products because by experience I can tell you that no matter what kind of support you have, when the things get nasty you better have very skilled people in-house and no official support will really save you (apart from your face).
A recent article by codecentric states as follows:
Apache Camel is a framework full of tools for routing data within an application. It is a framework you use when a full-blown Enterprise Server Bus is not (yet) needed.
You can find the full article here
Don't get too stuck in words like ESB and frameworks. The things that should decide on what kind of platform you need should depend on:
Your current and future system landscape
Your current and future requirements (technical and non-functional)
Your in house competence
Your budget
After going through those steps then you can evaluate and come to a conclusion on what you need .For some apache camel is the best fit for some other platforms may be a better fit. Don't get stuck in words like ESB etc.
I know this is not a programming question per se, but I wanted to get as much input from the SO community on a new project I hope to get started. The project is from being started from scratch and thus every decision for programming languages, databases, frameworks, platforms and what not are up in the air. I'm hoping to get your opinion on the matter, what you feel are the strengths and weaknesses of each option.
Database:
Currently I have the option of using MSSQL or MySQL. While I am leaning towards using MySQL because it is free and most probably has all the features I need. However, there is the possibility of having a lot of hierarchical data and the new hierarchical data type in MSSQL is quite appealing. Does it really simplify matters that much? Also MSSQL supports many more advanced SQL functions that may or may not be useful in the long run. While for development I can get access to Server 2008, multiple licenses as the development team grows and for production, are the costs justified?
Programming Languages:
The project will have a web based front end UI and a server based component that will do some heavy lifting.
For the web based UI, I was thinking of maybe doing Apache/IIS with PHP or IIS with ASP.Net in C#. I'd like to use a good framework to properly utilize good design patterns that should structure the code and development of the app. As well as make modifications in the long run easy to implement. I also want the GUI to look good and don't like the idea of buying .Net controls from component vendors. Instead I prefer the idea of using good CSS, and open sources like YUI and javascript to make the UI sleek.
For the server based component, I was thinking of using C#. I have no real development experience in C++ and I'd like good libraries and sufficient speed is good enough. However, while the web based UI and server based component is loosely coupled, there may be instances where the UI needs to communicate (call methods and what not) with the server based component and I want to pick languages/frameworks that will play nice with each other.
All suggestions on frameworks to incorporate are welcome.
Version Control:
I have had good experiences with SVN and a pretty bad experiences with TFS. I've never worked with GIT. Which do you think is better in terms of features as well as general developer familiarity. I want to pick something that other developers will know and not have trouble with.
I apologize if the questions are bit redundant or I'm not providing enough information or using bad terminology. I plan to edit and improve the question as I get feedback. Thanks!
EDIT:
Who: This would most probably be a startup formed of college students or junior developers. I want the project to utilize technologies that most people are familiar with or are easy to pick up.
What: I'd need hours and days to explain the solution. But in the end when you break it down, its a web based UI (think standard web app to just manage database data) that would be used to knowledgeable clients. The server based component would be very separate except for the fact that it should be able to communicate with the web app.
I can provide more information as required but I would appreciate an opportunity for users to answer and provide their ideas before you hastily close the question.
Obviously it depends a lot on specific requirements, but then again, even with those I probably wouldn't be able to tell for sure!
I've been working on a from-scratch project myself for a couple of months, and have generally found:
Choosing Microsoft for all the layers just goes down much easier (my subjective opinion). For example I would use C# for the UI, the back end, and use MSSQL for the database. Nothing at all wrong with non-Microsoft vendors, I'm no Microsoft fan-boy, I just struggle to get productive with unfamiliar tools. Depends where your experience lies though.
Database: In particular I've found that .NET and MSSQL go easily together. When I started the project I was using a PostgreSQL (because it's free, fully featured and has open-source warm fuzzies). However I abandoned it in favour of MSSQL simply because it was taking me too long to get database work done in an unfamiliar language with unfamiliar tools. Also, I'm not sure MSSQL is so expensive anymore, for example for a web application, MSSQL 2008 Web Edition is pretty damn cheap per-processor I think (only on SPLA licensing though). If you're concerned about database features in a free implementation though, personally I think PostgreSQL has a very full feature set, nicely standardised, and rapidly growing.
UI: I'm pretty inexperienced, but ASP.NET MVC looks far less painful to me than ASP.NET Web Forms. I like PHP too, but again I'd match the UI language with the back-end language, so would recommend .NET.
On frameworks, I'm immersed in DALs at the moment. I like Subsonic for lightweight data, NHibernate for heavy-weight.
I still have a long way to go with my project so perhaps I can only see the short-term benefits and drawbacks at the moment. But in general I would say: use the technologies that you're most comfortable using, as you'll be way more productive and the end result will probably be about the same anyway. If you want to learn new technologies though, and who doesn't? - go ahead, just expect it to take a lot longer.
Didn't want to answer 'cause it's so open ended. But a few points:
Money
First, check out BizSpark. That should take care of any money aspect for 3 years. For a service company, that means not only free VS Team Suite and Office and so on, but free Windows, SQL, etc. If your startup can't afford to spend a bit on MS tech in 3 years, it's probably a bad business. So that takes out licensing.
On a similar note, Sun has Startup Essentials. Could be interesting on the hardware side of things, but I haven't actually competitively priced them versus Dell/HP.
Software
It doesn't sound like you have hard enough requirements to say "oh, this slightly-less-popular software X is perfect for my domain Y and is gonna give me a very big boost". In fact, your project might not be like that at all. Maybe it, technically, is going to be a relatively plain application just pushing data around or whatever. You didn't specify.
For a small startup, personal productivity is probably going to trump any other argument. If your people are excellent in X, then that's one of your top arguments right there.
If you really don't have any particular system you're most comfortable with, be conservative. Stick with .NET or Java, as they'll give you the widest range of useful possibilities.
As far as things like OS and Database, I'm biased, but I think Microsoft will give you platforms that are easier to take advantage of than you'll find elsewhere. For instance, setting up load balancing, clustering, centralized authentication, managing servers (updates, events, etc.) is going to be easier to get going on Windows than it would be on another platform, assuming you're not an expert in either. Configuring SQL Server, even the advanced features, is a piece of cake. (Go time someone who knows neither: Setup a DB mirror in MSSQL and MySQL -- which is going to take more work?) Again, this is all predicated on you not having experts in a particular set of technology.
Don't mix -- whatever you do, stick with the platform. If you go .NET, MSSQL is going to work better with the data providers (or things like Linq-to-SQL). If you decide to do PHP, then use MySQL as everyone else uses it and you'll encounter less resistance. If you're not inventing stuff on the technical side, don't become an edge case.
You should pick the platform first, then the language that is best for that platform (if there is any choice).
One thing you should consider is the labor pool, and labor pool cost, for specific platforms and languages. Human Resources can often get cost metrics, if you don't have ideas already.
In my town, for example, .NET platform is much more expensive per Software Engineer than open source, because the .NET developers have a higher rate (40% roughly). C# is a little higher rate than VB.NET, but also tends to bring more well rounded candidates.
Just to throw in something totally different: How about weblocks as a web framework? It uses Hunchentoot as a server, which can run either standalone or with Apache. This is all done in Common Lisp. Weblocks can use cl-sql as a backend store, which can connect to many different RDBMs (MySQL, PostgreSQL, Oracle, ODBC, SQLite).
Our company has a point of sale system with many extras, such as ordering and receiving functionality, sales and order history etc. Our main issue is that the system was not designed properly from the ground up, so it takes too long to make fixes and handle requests from our customers. Also, the current technology we are using (Progress database, Progress 4GL for the language) incurs quite a bit of licensing expenses on our customers due to mutli-user license fees for database connections etc.
After a lot of discussion it is looking like we will probably start over from scratch (while maintaining the current product at least for the time being). We are looking for a couple of things:
Create the system with a nice GUI front end (it is currently CHUI and the application was not built in a way that allows us to redesign the front end... no layering or separation of business logic and gui...shudder).
Create the system with the ability to modularize different functionality so the product doesn't have to include all features. This would keep the cost down for our current customers that want basic functionality and a lower price tag. The bells and whistles would be available for those that would want them.
Use proper design patterns to make the product easy to add or change any part at any time (i.e. change the database or change the front end without needing to rewrite the application or most of it). This is a problem today because the Progress 4GL code is directly compiled against the database. Small changes in the database requires lots of code recompiling.
Our new system will be Linux based, with a possibility of a client application providing functionality from one or more windows boxes.
So what I'm looking for is any suggestions on which database and/or framework or programming language(s) someone might recommend for this sort of product. Anyone that has experience in this field might be able to point us in the right direction or even have some ideas of what to avoid. We have considered .NET and SQL Express (we don't need an enterprise level DB), but that would limit us to windows (as far as I know anyway). I have heard of Mono for writing .NET code in a Linux environment, but I don't know much about it yet. We've also considered a Java and MySql based implementation.
To summarize we are looking to do the following:
Keep licensing costs down on the technology we will use to develop the product (Oracle, yikes! MySQL, nice.)
Deliver a solution that is easily maintainable and supportable.
A solution that has a component capable of running on "old" hardware through a CHUI front end. (some of our customers have 40+ terminals which would be a ton of cash in order to convert over to a PC).
Suggestions would be appreciated.
Thanks
[UPDATE]
I should note that we are currently performing a total cost analysis. This question is intended to give us a couple of "educated" options to look into to include in or analysis. Anyone who could share experiences/suggestions about client/server setups would be appreciated (not just those who have experience with point of sale systems... that would just be a bonus).
[UPDATE]
For anyone who is interested, we ended up going with Microsoft Dynamics NAV, LS Retail (a plugin for the point of sale and various other things) and then did some (and are currently working on) customization work on top of that. This setup gave us the added benefit of having a fully integrated g/l system, which our current system lacked.
Java for language (or Scala if you want to be "bleeding edge", depending on how you plan to support it and what your developers are like it might be better, but also worse)
H2 for database
Swing for GUI
Reason: Free, portable and pretty standard.
Update: Missed the part where the system should be a client-server setup. My assumption was that the database and client should run on the same machine.
I suggest you first research your constraints a bit more - you made a passing reference to a client using a particular type of terminal - this may limit your options, unless the client agrees to upgrade.
You need to do a lot more legwork on this. It's great to get opinions from web forums, but we can't possibly know your environment as well as you do.
My broad strokes advice would be to aim for technology that is widely used. This way, expertise on the platform is cheaper than "niche" technologies, and it will be easier to get help if you hit a brick wall. Of course, following this advice may not be possible if you have non-negotiable technology already in place at customers.
My second suggestion would be to complete a full project plan, with detailed specs and proper cost estimates, before going with the "rewrite from scratch" option. Right now, you're saying that it would be cheaper to rewrite the system than maintain it, and you don't really know how much it would cost to re-write.
I suggest you use browser for the UI.
Organize your application as a web application.
There are tons of options for the back-end. You can use Java + MySQL. Java backend will save you from windows/linux debate as it will run on both platforms. You won't have any licensing cost for both Java and MySQL. (Edit: Definitely there are a lot of others languages that have run-times for both linux & windows including PHP, Ruby, Python etc)
If you go this route, you may also want to consider Google Web Toolkit (GWT) for creating the browser based front-end in a modular fashion.
One word of caution though. Browsers can be pesky when it comes to memory management. In our experience, this was the most significant challenge in doing browser based POS You may want to checkout Adobe Flex that runs in browser but might be more civil in its memory management.
What is CHUI? Character-UI, as in VT terminals? Or even 3270 style?
It sounds like you need a 3-tier system - the database backend, a middle-layer that runs the bulk of the back-end business processes, and a front-end layer for the CHUI / GUI / data-gateway.
All three layers can reside on one machine; or you can distribute the tiers out to various servers. The front-end layer would control the actual terminals, whether they are VT-terminals, or a web-browser, or a custom-written 'client' application.
Make sure you have considered the hardware needs here -- are you going to have barcode scanners, cash drawers, POS debit/credit terminals, et cetra? If you are using a standard browser, it might be hard to reliably integrate those items. (At the very least, you're likely going to have to write special applets to handle them.)
Finally, consider the possibility of a thin-client technology on Windows. It greatly simplifies system management, since you only have to upgrade the software centrally. Thin-client PC's are cheap -- sub $200.
Golden Code Development (see www.goldencode.com) has a technology that does automated conversion of Progress 4GL (the schema and code... the entire application) to a Java application with a relational database backend (e.g. PostgreSQL). They currently support a very complete CHUI environment and they do refactor the code. For example, the conversion separates the UI, the data model and the business logic into separate Java classes. The entire result is a drop-in replacement that is compatible with the original (users don't need retraining, processes don't need to be modified, the data is migrated too). This is possible because they provide an application server and a set of runtime classes that provide that compatibility. The result of the automated conversion is not something that needs further editing before you can compile and run it. True terminal support is included so hardware terminals still work (it requires a small JNI library to access NCURSES from Java). All the rest of the code in the runtime is pure Java. No Progress Software Corp technology is used in the resulting system and it runs on Linux.
At least one converted system is already in production, running a 24 by 7 mission critical environment. It is a converted ERP system that their mid-sized pilot customer uses to run their entire business.