Agile architecture means how enterprise / system / software architects apply architectural practice in agile software development. A number of commentators have identified a tension between traditional software architecture and agile methods along the axis of adaptation (leaving architectural decisions until the last possible moment) versus anticipation (planning in advance). (Kruchten, 2010 )

Waterman, Nobel and Allan (2015) explored the tensions between spending too little time designing an up-front architecture, increasing risk, and spending too much time, negatively impacting of the delivery of value to the customer. They identify six forces that can affect agile architecture: Requirements instability, technical risk, early value, team culture, customer agility and experience. These forces may be addressed by six strategies; Respond to change, address risk, emergent architecture, big design up front and use frameworks and template architectures.

Several attempts have been made to specify what makes up an agile approach to architecture. According to the SAFe framework, the principles of agile architecture are:

Design emerges. Architecture is a collaboration. (intentional architecture)
The bigger the system, the longer the runway (architectural runway)
Build the simplest architecture that can possibly work (established design principles)
When in doubt, code or model it out (spikes, prototype, domain and use case models)
They build it, they test it (design for testability)
There is no monopoly on innovation (teams, hackathons) – Facebook’s Like button was conceived as part of a hackathon
Implement architectural flow (architectural epics and the portfolio kanban) – the portfolio Kanban goes through funnel, review, analysis, portfolio backlog and implementing
At the Enterprise Architecture level, Scott Ambler (2016) proposes the following principles

Evolutionary collaboration over blueprinting
Communication over perfection
Active stakeholder participation
Enterprise architects are active participants on development teams
Enablement over inspection (exemplars)
High level models (the more complex, the more abstract)
Capture details with working code
Lean guidance and rules, not bureaucratic procedures
Have a dedicated team of experienced enterprise architects

Source From Wikipedia