Irish soldiers in Ceylon: The Royal Irish were there in 1835, I don't know when they first were there. In 1835, six companies were sent to China.
The number of Royal Irish troops was large in Ceylon in 1837, when they sailed for Madras. From there they went to China, where they played a prominent part in the First Chinese War of 1840-1842. From there, they returned to India. Sent back to China, they fought around Canton in 1847. Again returning to India*, the Regiment served in the Burmese War of 1851-52. In 1854, they joined the army in the Crimea, and were prominent at the siege of Sevastapol. By 1857, they were back in India, and served there until 1866. *I don't know if 'India' includes Ceylon, I haven't delved deeply enough to get details of where they were actually stationed.
Notes above are from the website of www.waterfordcountymuseum.org.

The Ceylon Rifles seemingly had some Irish members, but I have not looked into their records.
Several genealogical notes are from people seeking information about members of the Irish Regiment and their service in Ceylon.

Was any other place than "Sulloon" mentioned in versions of the song? If not, the fighting of the song could have taken place in India, China, and Crimea; Ceylon just where they were stationed before sailing to Madras in 1837, or perhaps stationed after service elsewhere.