The post featured a collage of photo booth pics of Moakler and Rondeau laughing and smiling, as well as one pic in which Moakler is planting a kiss on Rondeau's cheek. She captioned the post with a smiley face and kiss emojis.
On Thursday, Moakler shared another photo of herself and Rondeau to her Story that showed them sitting together on the deck of a boat, while enjoying a drink.
A source tells ET, "Shanna and Matthew are back together right now and in a good place. Their relationship has been on and off, but at this time, they're both doing really well."
Rondeau confirmed back in July that the pair had called it quits earlier in the year, telling ET in an exclusive statement that the split was "beneficial for the both of us."
Moakler and Rondeau, a model and actor, met on Instagram and have been dating off and on for about a year and a half, though ET's source said the pair likes to keep their relationship "somewhat private and low key. They like to spend one-on-one time with each other away from the public eye."
"Whenever they've taken time apart, they always end up getting back together and have a lot of love for each other," the source continued. "They like doing the same things and have the same goals for the future. Matthew is there for Shanna, and she is always there for him whenever he needs her."
The 42-year-old reality star and 45-year-old rock star got engaged on Oct. 17 in a stunning seaside proposal. Barker popped the question as the sun set, inside a heart made of red roses and lined with candles, on the beach at the Rosewood Miramar Beach hotel in California.