OS-level virtualization generates a minimal start-up and run-time overhead on the host OS and thus suits applications that require both good isolation and high efficiency. However, multiple-member applications required for forming a system may need to occasionally communicate across this isolation barrier to cooperate with each other while they are separated in different VMs to isolate intrusion or fault. Such application scenarios are often critical to enterprise-class servers, HPC clusters and intrusion/fault-tolerant systems, etc. The authors make the first effort to support the inter-application interactions in an OS-level virtualization system without causing a significant compromise on VM isolation. They identify all interactive operations that impact inter-application interactions, including inter-process communications, application invocations, resource name transfers and application dependencies.