Legacy System Replacement

on Mar18


A lot of already-established companies are still using solutions, based on legacy software that was developed using mainframe systems. Many of these companies want to switch to newer solutions from archaic older ones. However, the process presents certain difficulties.


A company is using a legacy system, which performs all the critical payment handling functions for the company. The system is strategically important, because all company’s business operations revolve around it. The company needs an efficient way to migrate to the new solution.


While it often seems obvious that an old system needs to be replaced with a new one, the actual implementation of the new system is a very challenging process. Let us suppose, there is a legacy system, used by some organization. The legacy system has many integrations with banks and other entities. Also, many front-end systems (such as POS and CRM systems) are connected to the legacy system. A lot of data of various kinds (merchant data, transaction data, etc.) is stored in the system. Certain rules, implemented in the legacy system, are not always trivial or obvious. People, who implemented them, might no longer be working with the company. At the same time, the system is used by the whole company and many vital operations rely on it.

Strategy in brief

As we can see from the previous section, the main question is how to migrate all the integrations, business logic, and data to the new system. Keep in mind that some new logic and business processes might have to be added to the new system during the migration.

The main issues to be addressed in the context of transition from the legacy system to the new one are:

  • PCI compliance
  • Integrations with processors
  • Integrations with front-end systems
  • Personnel training
  • Data migration

In the next section we are going to describe the steps, addressing each of these issues one by one.

Strategy in detail

In fact, there are several options a legacy system user can follow. We are going to use the example of one of our clients, which faced the problem of legacy system replacement and successfully managed to solve it.

Environment preparation

The first thing you should do is prepare PCI environment and install the respective software into this environment. If hosted environment is used, then all the respective hardware and software has to be provisioned into the cloud platform.

Optimization of integrations with processors

You should decide, which integrations have to be implemented to enable real-time and batch processing of transactions, account updater, chargeback handling, and merchant on-boarding. Possibly, you have to sunset some of the existing integrations, if the number of merchants using these integrations is relatively small. These merchants will have to be migrated (transferred) to the new platform, terminated, or temporarily retained on the existing platform.

In other words,

  • transaction volumes have to be analyzed,
  • based on this analysis, the key platforms for future integrations should be selected,
  • the future of the existing integrations with low-transaction-volume platforms should be decided. You should decide whether the migration is worth the effort, as certification of each new integration is a time- and labor-consuming procedure (see, for example, article on EMV certification for details).

Analysis of integrated systems

You should conduct the analysis of all the front-end systems, integrated into the existing payment gateway, and decide, whether these integrations are relevant for the new product.
Front-end systems include POS systems, CRM systems, web-sites and online services, that process payments through them, any mobile terminal solutions, or any other systems, that submit transactions into the legacy system for processing.

Just like in the case of merchants and processors, the options are: to migrate the systems, to leave them temporarily integrated with the old platform, or to phase them out (as legacy products used by a very small number of clients).

Once the inventory of the integrated systems is taken, and the decision is made as to which of them must be re-connected with the new system, the most appropriate re-integration strategy must be worked out.

Fundamentally, there are two ways to accomplish this.

  • Integrate the new system with the new payment processing system using the new system’s standard (native) API. This implies changes made in the front-end system and may not be appropriate for cases when the front-end system can no longer be modified.
  • For cases when it is not desirable to change the front-end system, an emulator of the legacy system’s API can be implemented in the new system. This way the news system will be able to accept transactional information from the front-end systems in legacy format that was used before.

Analysis of the business processes

The next important thing to do is analysis of all the business processes (and how they are performed) with the operations team. The business processes include merchant on-boarding, reviewing of files, settlements, funding, reconciliation of deposits, and others. Equivalents to these processes should be found within the new gateway. Gaps should be identified and plans should be worked out for implementation of the respective new logic. Sometimes, the logic might be already in place, but additional training materials are required, in order for the team to be able to use them for reference while working with the new system.

Development of data migration strategies

The next step to take is to decide, how the data is going to be migrated. The relevant data, usually, includes

  • Merchant settings (MIDs, settlement times, etc.)
  • Tokens (payment information, which might be used in future)
  • Recurring billing schedules (payment plans)
  • Transactional activity (statements, transactions)

You should define the ways of handling each of these data types.

Merchant settings, generally, have to be migrated. Migration is, usually, done through API or file formats of the existing gateway. It is preferable for the mechanism to allow you to transfer the merchants from one platform to another one by one. If transition goes flawlessly for one or two merchants, other merchants can be moved as well. Ideally, you should devise an approach, allowing you to add new merchants to the new system, and, at some point, import all of the existing merchants into it. Keep in mind, that the information of a merchant might get changed before it goes live on a new system and some manual adjustments after the import process might be necessary.

Tokenization data requires special attention. Tokenization data is not always readily available. Sometimes the tokens are stored by the processor and extraction of the data has to be ordered in advance. A special process might be required for conversion of tokenization data from one vault to another (re-tokenization). The tokens will have to be updated with the already existing systems. If tokens cannot be updated, you need to devise a strategy for token mapping with the new values in the existing gateway. As you are dealing with tokenization, PCI compliance issues will also have to be addressed.

Recurring billing data has to be addressed separately, because billing history and balances might be required for future analysis.

As for transaction data, in most cases there is no need to migrate it (although, sometimes, when recurring billing is involved, migration is necessary). If necessary, the respective reporting documents with transaction data can be found in the old database. If the data has to be transferred, a separate strategy is needed for the transfer. If the API is available, transaction data transfer can be performed through the API, if not – migration should be done at the database level.

Preparation for PCI audit

If PCI compliance remains the responsibility of the company, originally owning the legacy system, it needs to prepare all the documentation, necessary for the future PCI audit. It is easier to record all of the procedures at the initial development phase and analyze all of the PCI consequences at that time.


Before replacing your legacy system with a new one, you should gather the information on the transition process and devise a clear system replacement strategy.

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